Embarrassingly, I reported a bug that was in fact my own doing.
How can I safely remove the 11.0~git packages and replace them (if necessary) with Ubuntu provided mesa as suggested in the comment on the bug report?
I tried selecting them all for removal but they want to take out nearly every package in the system along with them.
I believe (although not certain) that they came from this repo I see in the list, disabled during the upgrade:
$ sudo ppa-purge ppa:paulo-miguel-dias/mesa
Updating packages lists
PPA to be removed: paulo-miguel-dias mesa
Warning: Could not find package list for PPA: paulo-miguel-dias mesa
The offending PPA seems to be http://ppa.launchpad.net/paulo-miguel-dias/mesa/ubuntu
ppa-purge
.