This seems to happen because TrackPopupMenu returns as
soon as the WM_LBUTTONDOWN is received. That message is
correctly purged. The problem comes from the subsequent
WM_LBUTTONUP message.

This patch is not a clean solution, but keeps the problem local.



[2. text/plain; patch.diff]...

To confirm, is the bug report related to 24.0.50, a rather old version?

Have you checked if this bug is present in a recent version of Emacs?

Yes, it is present in current version.