For short term, this has been fixed by replacing the libmysqlclient18{,-dev} in repo with PS's ones, this works because
dpkg --compare-versions 5.5.34-rel32.0-591.precise gt 5.5.34-23.7.6-565.precise && echo true true
and also because libmysqlclient18 is essentially the same in both.
For long term, this requires changes in packaging and should be a release blocker.
For short term, this has been fixed by replacing the libmysqlclient1 8{,-dev} in repo with PS's ones, this works because
dpkg --compare-versions 5.5.34- rel32.0- 591.precise gt 5.5.34- 23.7.6- 565.precise && echo true
true
and also because libmysqlclient18 is essentially the same in both.
For long term, this requires changes in packaging and should be a release blocker.