Comment 8 for bug 1608236

So 4.4.0-22 has the bug, but 4.4.0-31 does have the bug? From your testing of upstream 4.4.17 in comment #4 this sounds like it is related to an Ubuntu specific SAUCE patch. This would be confirmed by your test results of the -proposed kernel.

We can perform a kernel bisect to identify the commit that introduced this regression. We first need to identify the last good Ubuntu kernel and the first bad one. If -22 is good, we probably want to test 4.4.0-29 next. It can be downloaded from:

https://launchpad.net/~canonical-kernel-team/+archive/ubuntu/ppa/+build/10184098