It is a mce bug.
mce sends a signal to systemui when the power button is pressed, then systemui shows the power menu button. Also, mce is responsible for dimming, and mce is related to alarmd.
I've suffered this issue before installing ASUI, and I have done may be a hundred tests trying to find a workaround or a fix before finally giving up.
Since mce has nothing to do with the kernel, it is not caused by the kernel (or otherwise many programs would crash or exhibit other symptoms).
It is caused by a race condition (http://en.wikipedia.org/wiki/Race_condition) in mce, probably related to gconf. The relation of the kernel here is that, for the different timing caused by the different schedulers, this mce bug is exposed when using other schedulers than O1.
How do I know that?
I saw it appear with the first alpha kernels, with both CFS and the SD schedulers, preemption or not. So it happens with two different schedulers, and the only thing affected by a scheduler is timing.
With the new gconf packages (which also have increased performance) it disappeared for me.
So yes, DT may expose this bug, and I can do nothing to fix it, short of rewriting the whole mce thing because it is closed source.