This is a bug, and should be reported as one. If you find (or someone else reports) an effective workaround, that can be included in the bug report. As per the FAQ, bugs are off-topic on Ask Ubuntu, so the only part of this question that should really be addressed here is the issue of how to report this bug. Detailed work and troubleshooting on bugs in Ubuntu needs to happen on Launchpad; otherwise, valuable work tends to be ignored and fragmented.
Power management functionality is part of the kernel, so the correct way to report this bug is to run
ubuntu-bug linux. Detailed technical information will be sent to Launchpad, but you will still have to describe the problem, including anything you've tried and what happened, in as much detail as possible.
One common mistake is to report power management bugs against the
acpi package. That's not the right way, since the
acpi package doesn't actually perform any power management; it's just an interface for getting information about the power management that is happening in the kernel (Linux).
I recommend that you:
- Trigger the problem.
- Record the time that you triggered it.
- (Re)boot your Ubuntu system.
- Once booted back up, immediately report the bug.
- Indicate that you have done all this in your bug report, and specify the time (or approximate time) you triggered the freeze.
That may make it easier for triagers, developers, and other interested persons to identify entries in automatically attached log files that pertain to the problem.
It's a very good idea to read this thoroughly before reporting this or any other bug in Ubuntu. This question is also often quite helpful.
Finally, please note that if you are reporting this bug against the downstream kernel (linux in Ubuntu, reporting on Launchpad, as described here), you must be running (and you should have last produced the bug using) this version of the kernel, and not a custom-built or upstream kernel.org version.
If you report this bug or find it already reported, feel free to subscribe me to the bug if you wish.