Comment # 14 on bug 110865 from Alex Deucher

(In reply to Dieter Nützel from comment #13)
> 
> Alex, is this the same problem?

No.

> 
> GFX Clocks and Power:
>         300 MHz (MCLK)
>         300 MHz (SCLK)

Your mclk is going to a lower state when it's idle.