Comment 14 for bug 30557

I can comfirm (thanks to Davyd's tip) that this problem is indeed related to C-states.

Setting the max cpu C-state to C2 (it spends most of it's time in C3 by default) using:

echo 2 > /sys/module/processor/parameters/max_cstate

Causes the /proc/stat values start to increase by reasonable values and more importantly cpufreq_conservative actually starts to scale the cpu speed when idle.