Comment 3 for bug 1858164

It seems this is a side effect of a mistake made in the release and subsequent withdrawal of update 1:11.1-1ubuntu7.5. So it's not a bug in the code but is a problem people will encounter with Ubuntu updates...

This should automatically correct itself with the re-release of 1:11.1-1ubuntu7.5. In the meantime you can manually install whichever set of packages you need from either:

1:11.1-1ubuntu7.4: https://launchpad.net/ubuntu/+source/pulseaudio/1:11.1-1ubuntu7.4/+build/17893827

1:11.1-1ubuntu7.5: https://launchpad.net/ubuntu/+source/pulseaudio/1:11.1-1ubuntu7.5/+build/18146190