Turns out that the X11 adventure is not over yet.

I've noticed a while ago that Bitmap had a very odd appearance under modern Ubuntu, mirroring the weirdness from oclock and xlogo.

This time, taken by a sudden surge of braveness (no doubt, fueled by my recent work with the mesa demos), an issue was filed. The maintainer was very kind to explain to me the root cause of this oddness. I wasn't all that far in my assumptions, but was looking at the wrong place (at least in the case of Bitmap).