The assignment of Str := TComboBox.text fails, when drowdownstyle is eg. csDropdownlist or csDropDownDrawFixed (it works only with style csDropDown)
Workaround is to use
if TComboBox.itemindex <> -1 then begin Str := TComboBox.items[TComboBox.itemIndex]; end;
But it is hard to locate all this places and make this changes, so I would prefer to have it work as expected on all platforms (and this is a kind of hidden bug for the developper, the program runs, but acts different on linux and mac).