When I set the groupbox parameter to false True, the mention of this property disappears in the * dfm file (see attachment).
That's normal, if the default state is True; properties in their default state are (usually) not included in the lfm
It seems to me that in Linux this line should be ignored. I think this is a bug.
Yes, if it not supported in a given widgetset it should be either silently ignored or a warning (not an error!) about the unsupported state given ( don't remember which, sorry). Unfortunately I've not got a trunk install here to test, sorry again.
Let's hope someone with more knowledge than I chimes in ...