I have had the shutdown issue twice on my N810 (not with this new kernel but just with the d-t packages).

These times the power button wasn't working with the "screen won't go off" issue too.

So maybe these issues are relationated???

When that happened advance-power option to shutdown the device just rebooted. Same second time to shutdown with the advance-power menu.

Third time all went fine. Advance-power option could shutdown N810, screen go off allright and device power button worked again.

So I think all these issues are different sides of the same problem.