Erro ao inflar o botão de classe no Android

Eu tenho um aplicativo com min sdk 16 até 23. Quero usar o design de materiais o máximo possível. Ele também deve ser um aplicativo em tela cheia. A biblioteca de suporte do AppCompat está incluída. Agora eu tenho atividade de logon com alguns botões:

<Button
    android:id="@+id/act_logon_btn_logon"
    style="@style/ButtonDefault"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="@string/act_logon_logon" />

Os estilos são os seguintes (values / styles.xml):

<style name="Theme.AppCompat.Light.NoActionBar.FullScreen" parent="@style/Theme.AppCompat.Light">
    <item name="windowNoTitle">true</item>
    <item name="windowActionBar">false</item>
    <item name="android:windowFullscreen">true</item>
    <item name="android:windowContentOverlay">@null</item>
</style>

<style name="AppThemeBase" parent="Theme.AppCompat.Light.NoActionBar.FullScreen"></style>

<style name="AppTheme" parent="AppThemeBase"></style>

<style name="ButtonDefault" parent="Widget.AppCompat.Button">
    <item name="android:textSize">?attr/font_medium</item>
</style>

<style name="FontStyle"></style>

<style name="FontStyle.Small">
    <item name="font_small">12sp</item>
    <item name="font_medium">14sp</item>
    <item name="font_large">16sp</item>
</style>

<style name="FontStyle.Medium">
    <item name="font_small">16sp</item>
    <item name="font_medium">18sp</item>
    <item name="font_large">20sp</item>
</style>

<style name="FontStyle.Large">
    <item name="font_small">20sp</item>
    <item name="font_medium">22sp</item>
    <item name="font_large">24sp</item>
</style>

E em valores / attrs:

<declare-styleable name="FontStyle">
    <attr name="font_small" format="dimension" />
    <attr name="font_medium" format="dimension" />
    <attr name="font_large" format="dimension" />
</declare-styleable>

Atributofont_medium é definido como descritoaqui. O comportamento que não entendo é que, quando a atividade de Logon é aberta, tudo está bem, sem exceções. Mas quando abro outra atividade da atividade Logon com fragmento interno e o fragmento possui um botão com esse estilo, recebo uma exceção dizendo "Erro ao inflar a classe Button". Quando eu apago oTamanho do texto atributo do estilo ButtonDefault, tudo funciona. Por que funciona em algum lugar e em algum lugar não? Há algo de errado com o atributo personalizado?

Eu tentei criar values-v21 / styles.xml com esse estilo, mas sem efeito.

Você também pode explicar as diferenças entre as seguintes definições de estilo pai? Eu estou me perdendo.

parent="Widget.AppCompat.Button"
parent="@style/Widget.AppCompat.Button"
parent="android:Widget.Button"
parent="android:Widget.AppCompat.Button"
parent="android:Widget.Material.Button"
parent="android:style/Widget.Material.Button"

Obrigado.

EDIT 1 - exceção:

12-17 10:56:53.950: E/AndroidRuntime(7251): FATAL EXCEPTION: main
12-17 10:56:53.950: E/AndroidRuntime(7251): Process: test.android, PID: 7251
12-17 10:56:53.950: E/AndroidRuntime(7251): java.lang.RuntimeException: Unable to start activity ComponentInfo{test.dci.android/test.dci.android.view.activity.TransactionActivity}: android.view.InflateException: Binary XML file line #49: Error inflating class Button
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2702)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2767)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.app.ActivityThread.access$900(ActivityThread.java:177)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1449)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.os.Handler.dispatchMessage(Handler.java:102)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.os.Looper.loop(Looper.java:145)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.app.ActivityThread.main(ActivityThread.java:5951)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at java.lang.reflect.Method.invoke(Native Method)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at java.lang.reflect.Method.invoke(Method.java:372)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1400)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1195)
12-17 10:56:53.950: E/AndroidRuntime(7251): Caused by: android.view.InflateException: Binary XML file line #49: Error inflating class Button
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:770)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.view.LayoutInflater.rInflate(LayoutInflater.java:813)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.view.LayoutInflater.rInflate(LayoutInflater.java:821)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.view.LayoutInflater.inflate(LayoutInflater.java:511)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.view.LayoutInflater.inflate(LayoutInflater.java:415)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at test.dci.android.view.fragment.TransactionFragment.onCreateView(TransactionFragment.java:71)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.support.v4.app.Fragment.performCreateView(Fragment.java:1962)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1036)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1226)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.support.v4.app.FragmentManagerImpl.addFragment(FragmentManager.java:1328)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.support.v4.app.FragmentManagerImpl.onCreateView(FragmentManager.java:2284)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.support.v4.app.FragmentController.onCreateView(FragmentController.java:111)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.support.v4.app.FragmentActivity.dispatchFragmentsOnCreateView(FragmentActivity.java:314)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.support.v4.app.BaseFragmentActivityHoneycomb.onCreateView(BaseFragmentActivityHoneycomb.java:31)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.support.v4.app.FragmentActivity.onCreateView(FragmentActivity.java:79)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at test.dci.android.view.activity.TransactionActivity.onCreateView(TransactionActivity.java:1)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:740)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.view.LayoutInflater.rInflate(LayoutInflater.java:813)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.view.LayoutInflater.inflate(LayoutInflater.java:511)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.view.LayoutInflater.inflate(LayoutInflater.java:415)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.view.LayoutInflater.inflate(LayoutInflater.java:366)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.support.v7.app.AppCompatDelegateImplV7.setContentView(AppCompatDelegateImplV7.java:256)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:109)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at test.dci.android.view.activity.TransactionActivity.onCreate(TransactionActivity.java:31)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.app.Activity.performCreate(Activity.java:6289)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2655)
12-17 10:56:53.950: E/AndroidRuntime(7251):     ... 10 more
12-17 10:56:53.950: E/AndroidRuntime(7251): Caused by: java.lang.RuntimeException: Failed to resolve attribute at index 12
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.content.res.TypedArray.getDimensionPixelSize(TypedArray.java:582)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.widget.TextView.<init>(TextView.java:1400)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.widget.Button.<init>(Button.java:115)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.widget.Button.<init>(Button.java:108)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.support.v7.widget.AppCompatButton.<init>(AppCompatButton.java:62)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.support.v7.widget.AppCompatButton.<init>(AppCompatButton.java:58)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.support.v7.app.AppCompatViewInflater.createView(AppCompatViewInflater.java:98)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.support.v7.app.AppCompatDelegateImplV7.createView(AppCompatDelegateImplV7.java:938)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at android.support.v7.app.AppCompatDelegateImplV7.onCreateView(AppCompatDelegateImplV7.java:992)
12-17 10:56:53.950: E/AndroidRuntime(7251):     at 

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