I have main window and subclassed groupbox which has misc. controls as it's child windows (not subclassed). To get the correct message processing i have corrected the msg procedure address for the groupbox (SetWindowLong). However after call to the SetWindowLong the groupbox control disappears, but the child controls are shown and manipulate messages correctly. It looks like the groupbox is there, but just not visible. Does anyone have idea what makes it disappear or how to fix this?