Estoy cometiendo un error trivial aquí, pero no puedo entender cuál es el problema.

Necesito obtener la fecha del lunes de la semana de una fecha aleatoria. Parece que obtengo algo bastante diferente.

mydate <- date("2013-11-05")

format(mydate, "%A")           # this is Tuesday, right
#[1] "Tuesday"
month(mydate)                  # Month November, right
#[1] 11
myyr <- year(mydate); myyr     # year is 2013, right
#[1] 2013
day(mydate)                    # day number is 5, right
#[1] 5 
mywk <- isoweek(mydate);mywk   # weeknumber is 45, right (yes, not US convention here)
#[1] 45
format(mydate, "%V")           # weeknumber is 45, right as well
#[1] "45" 
# Monday of week 45 is 2013-11-04 but strptime following gives something else...

strptime(paste0(myyr, "Monday", mywk), "%Y%A%V")
#[1] "2013-11-19 EET" 
# and for checking

strptime("2013Monday45","%Y%A%V")
#[1] "2013-11-19 EET"

Gracias por adelantado