I'm trying to fix a problem in an existing application where <SHIFT><CTRL><TAB> correctly cycles through the MDI child windows, giving focus to each in turn. The problem appears for <CTRL><TAB> - this also cycles through the windows, but hides each window as it loses focus.

I'm running VB6 SP5. Has anyone got any ideas as to what may be causing this? I've been unable, so far, to recreate the problem in any other application.