consistent hibernation failure with kernel 3.12-1-rt-amd64

[Zenaan Harkness <zen@freedbms.net>]

So whilst wrangling with audio-dropouts, I installed:
Linux x220a02 3.12-1-rt-amd64 #1 SMP PREEMPT RT Debian 3.12.6-2
(2013-12-29) x86_64 GNU/Linux

and now, every time I choose hibernate from the XFCE gui, or run
pm-hibernate cmd, instead of hibernating, the monitors go off, and
then my laptop power button led starts flashing, and machine is hung -
5s press on power button i.e. hard reset is only way to reboot - no
hibernation.

Any ideas how I might be more specific in my debugging?

I was about to file a bug, but there's a new kernel out, so I'll try that first.