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This problem can be duplciated with the ProfStudio example.

• Run ProfStudio in the debugger (I deleted the registry entries first so that the window positions/settings would be the default)


• Drag the "Command Window" tab from the docked pane directly under MDI window and make it a floating window.


• Drag the "Properties" tab from the docked pane directly under MDI window and dock it to the floating "Command Window" window. It doesn’t matter if you dock it as a tab or as a regular pane.


• Drag the floating window with the "Command Window" and "Properties" panes and try to dock it back to the original pane under the MDI window, so that they become tabs again.

The program will crash with the following message:

Unhandled exception at 0x00582f60 (ProfUIS223nd.dll) in 
ProfStudio-nd.exe: 0xC0000005: Access violation reading location 
0xfeef014a.

in ExtControlBar.cpp, _DraggingStart(), at line 8692.

It looks like the m_hWnd variable is no longer valid.

As a follow-up, I put the following code at line 8687, and it fixed the problem

if (!::IsWindow( m_hWnd ) || !::IsWindow( msg.hwnd ))
   return;

Dear Kishore,

Thank you for these comments. This bug also may occur when dragging dynamically created tab-container bars which may be destroyed during drop operation. We have added IsWindow() check points into CExtControlBar::_DraggingStart().