XP Menu/ComboBox Problem

I developed an app on an XP machine - Midi Form with subforms etc. I use some API to color the menu bar white. It looks fine on the development machine (of course). So far, on two XP machines I've installed it on, at a certain point the menu will turn solid black, you can only see the text if you mouse over. Also, certain combo boxes when the drop down is displayed - the dropped down list "burns" onto the status bar of the midi form and the taskbar of windows. So, it kind of looks like the combo box is still open.

Has anyone run into anything similar?

I haven't had that problem so far.... maybe it's a Zorder problem??.. some object is in front of another and since the Zorder isn't defined (???) it does "strange stuff"!!

maybe some pictures to understand what's happenning...