I haven't had luck rebuilding libx11-6 without xcb on Ubuntu due to my lack of experience dealing with debian scripts; hopefully an Ubuntu developer can take a look and do a better job.
Other users have confirmed the problem (see launchpad's bug, linked above) and experienced the same results as I had with downgrading libx11-6 and libx11-data.
Just a little note,
I haven't had luck rebuilding libx11-6 without xcb on Ubuntu due to my lack of experience dealing with debian scripts; hopefully an Ubuntu developer can take a look and do a better job.
Other users have confirmed the problem (see launchpad's bug, linked above) and experienced the same results as I had with downgrading libx11-6 and libx11-data.