I have 3 child forms arranged in 2  MDI Tab groups.
The upper tab group contains Child A. The lower contains Children B and C.

If I repeatedly press Ctrl+F6 focus moves between the child client areas as expected.
[A > B > C > A ... ]

The problem is that when it moves from C to A (ie. from one tab group to the other) the client area displayed in the lower tab group ALSO changes. Instead of continuing to display the contents of child C it is now displaying the contents of child B, but the Active tab is still for child C. 
In other words the content of the tab changes but the tabs themselves are not redrawn.

Clicking on either the tabs or the content (in the B/C group) immediately brings everything back into sync.

I am not handling any Lost/Got focus events so I dont see how my code can be causing this.
(In fact I dont think my code should be allowed to force the tabs out of sync with their content anyway)

Any ideas?

Thanks
Mike