Comment 5 for bug 40243

The problem is that acpi does not start, and apm starts instead. X (or something else) does not work well with APM sleep (which is apparently what the button does then) and things break.
I guess reboot=b (wherever it should be added) would not help me because the system is stuck at a point where something is still running. I can type on the console and even try to run commands.

Adding acpi=force on the kernel command line solves the problem for me completely. The system does the same as the old kernel did.

Thanks