I am currently developing an application that requires updating parts of multiple views simultaneously. As the updates are time-critical, it is not possible to update the entire view on each 'OnUpdate' call, however this seems to lead to the parts of each view that are not being updated being blanked out instead. Is there a windows flag that indicates whether the view has not been redrawn properly that I could poll to see whether I need to do a full redraw? The view can be recovered by dragging one of the other views over it. Is this a common problem?