RC6 for an Intel GU doesn't always work

Sometimes - after a reboot or after wakeup from s2disk I'm observed at my ThinkPad T420 (i5-2540M CPU) w/ integrated intel graphic (i915 module) since 3.6-rc(5?), that the temperature is above 80°C (usually it is around/lower than 50 °C). Powertop-2.1 shows, that the all 4 CPU cores are mostly idle, but the GPU is running at 100%. It looks for me that the power saving mode RC6 isn't active.

After 1-2 s2ram's however the issue went away.

I'm observing the issue both under my Gentoo Linux and under a RH system (kernel 3.6.1 each).

It is hard to bisect b/c not reliable.