Hmm.  https://www.x.org/wiki/Development/Documentation/SubmittingPatches/ indicates that FreeDesktop.org Bugzilla is the place to submit X bugs... But https://bugs.freedesktop.org/createaccount.cgi says clearly that that Bugzilla is "ONLY for reporting bugs on the Mesa, Piglit, and Linux kernel graphics support projects".   ¯\_(ツ)_/¯