show up of context menu breaks window invalidation

Hi everyone,
     I have a CXTPToolBar on my window. I first right-click on the CXTPToolBar to show the context menu. The weird thing happens then. When I resize the window bigger,there are some strips along the resizing path.The width of the strip is the same as the width of my scrollbar. It seems the OS can't handle the invalidation properly after once the context menu is shown on the CXTPToolBar.
       Additionally,I use an overlay window to cover the whole area of my actual window to hide drawing when resizing. The reason is to prevent flicking problem when redrawing everything on my actual window. I think
it might relates with the overlay, because the problem only happens when I apply the overlay when resizing.
       I suspect, is the inner implementation of CXTPToolBar would lock some resources when showing the context menu. And later when I call ::UpdateLayeredWindow API which would require that kind of resources then fail to get,thus cause the drawing problem.
       I have been stumpled by this problem for a week. I appreciate anyone can give some hint on it.

Many Thanks!