It's definitely the xorg-server-1.20.11-1 package that's causing trouble. I'm not sure what the bug reporting procedure is, is there someone I should be emailing log files to?
Thanks for taking a proactive approach GroundedGrid.
If possible, Arch provides unaltered software from upstream projects. Therefore, bug reports are also directed upstream; in case of X.org, the relevant information is summarized here.