Who is parent for these new controls?
Could it be that there is a kind of race condition that causes problems when setting properties of the just created controls before the messageloop had been processed? That is basically the only difference I could think of between the four “normal” classes and the fifth one that derives from one of the other four…
May be you must implement some conditions, but I can't say more detailed because I have not enough info about your situation. If you can use TeamViewer then may I can connect to your PC and see it by self? It may be a fastest way to solve a problem.