Rectangular selection appears to be broken

I can't make rectangular selections work in the native NT version of XEmacs 21.2 built from the CVS archive as of just after midnight on 4/4. When I do a meta-button1 drag the rectangular selection highlights ok, but as soon as I release the mouse it disappears (both the highlight and the selection). I tried this with -vanilla and it still doesn't work, so it's not my customization. I took a quick look at mouse.el, but nothing obvious jumped out at me. If no one has any bright ideas, I'll try to look at this later, but I don't have time right now to dig into it more. Mike