Hey you have lost my flag!
It is not exactly a bug, but the way PellesC works
After the first compilation from porc util any change made with rc editor modify the rc file removing what it don't understands...
As a workaround you can include all flags and then exchange the one you want in the code.
I.e.
RC file
IDR_ICO_FR_FLAG ICON "French.ico"
IDR_ICO_IT_FLAG ICON "Italia.ico"
A Language def file:
#ifdef __FRANCE__
#define IDR_ICO_FLAG IDR_ICO_FR_FLAG
#else
#define IDR_ICO_FLAG IDR_ICO_IT_FLAG
#endif