Window Library 9SE

[Seiss Wagner]

I am using the 9SE library and I am trying to configure a 4" wood casement window frame in a 6" wood wall with a dry wall return at the jambs and head with a wood stool and apron at the sill, a most common application. However, every time I turn off the jamb extension setting the wood frame of the window re-sizes to the thickness of the wood wall eliminating the dry wall return. Is this a bug or a feature? Am I missing a setting? Whichever, I can't properly configure the window.