Hello, Peter.

Becouse your name is in last revision (1.12) of wincontrol.inc, and becouse I couldn't find who is maintainer of TWinControl at Lasarus web page, I address to you.

I've read code and found smth strange in
Procedure TWinControl.AlignControl(AControl : TControl);

Everywhere in code such construction used: TControl(Owner) But it seems to me that it's wrong and Parent should be used instead. There are difference between Parent and Owner
Parent - visual entity which have our TWinControl as one of children Owner - container which has ownership relation to our TWinControl. For example, Owner will Destroy our TWinControl when in his destructor. And Owner can be non-visual component (not derived fron TControl).

Maybe this can be of use for you.
Or maybe conception of Parent/Owner is not working now in Lasarus.

BTW, who is maintainer (main developer) for TWinControl