I may have incurred in a small resizing bug of CExtMiniDockFrameWnd, which seems to happen when a floating toolbar has a width larger than _mp.m_rcWorkArea.Width in CExtMiniDockFrameWnd::OnSize.
It can be reproduced as follows (e.g. starting from the MDI sample):
1) add buttons to make the toolbar very large:
for (int k=0;k<10;k++)
m_wndToolBar2.InsertButton(-1,ID_VIEW_LIKE_STUDIO_2005);
2) move the floating toolbar to the left so that most of it is outside the left border of the screen
3) drag its right border to make it layout as a single row.
The final result should be similar to this screenshot: http://www.babaschess.net/tmp/toolbar_bug.png
The problem seems to be caused by a WM_SIZE with a (probably) negative height (which is interpreted as a very large height) being sent to CExtMiniDockFrameWnd while it is already processing a WM_SIZE (this second WM_SIZE seems to be originated from the MoveWindow(&rcWnd) call inside the CExtMiniDockFrameWnd::OnSize handler, but I was not able to debug it better.