Hi Wiek,
Good find.
I reproduced several errors with the RAF and RCAF fonts when enabeling those options. And likely other fonts we share are designed in a simple way so they do not support those font properties.
Errors I got were:
andCould not complete your request because of a program error
After I did succesfully enter a font with properties like Bold or Italics.Font engine could not be initialised
Sometimes I got erratic behaviour like letters not appearing etc.