The shell's own dialogs (Taskbar and Start Menu Properties, Run, Shut Down, Search...) showed garbage -- stripes of the dragged window's caption -- where they were uncovered while another window was being dragged over them, or when they were pulled out from under the taskbar. The window manager's drag loop dropped the exposure event on the floor; it now hands events on the shell's own windows back to the toolkit, which repaints at once.
curl -sL jacktulli.github.io/w2k | sh