Redraw bug on Windows native build

Hi, I'm relatively new to XEmacs, so apologies if this issue is already known - I did search the archives and couldn't find an obvious reference... The native build of 21.2.20 on Win32 has a redraw bug. I checked 20.2.19, and the bug isn't in there, so it appeared between 19 and 20. To demonstrate the bug, just start 21.2.20, and then immediately drag the right hand edge of the window out. The newly exposed area doesn't redraw. Actually, it does redraw a few seconds later. I haven't any experience with the XEmacs sources, so I'm afraid I don't know where to begin to look for a solution. Also, I haven't got CVS access set up, so I can't check whether it's been fixed since 20. Hope this is useful, Paul Moore.