CPU cores not used ??

Ok i switched temporaly to GPU rendering to see if it would handle the textures better (faster).
But it didnt on my system so i went back to cpu…however

Despite blender correctly detects 8 cores, and i have set rendering to supported and fixed 8 cores.
Only 1 core in taskmanager is at 100% the average cpu utliziation is at around 11% as the other 7 cores are not used by blender. I’ve never seen this before blender 2.71 off release. is there something i’ve done wrong ?.

i’ve restarted blender, opened other blend files, no effect, its the last core that is used and the other cores are not used. I’m rendering using cycles.

>posting update > wondered if my blender was broken, i tried another beta blender (from the metropolis branche), i used normal cycles rendering again , but again, when looking in taskmanager, i only see one core utilized to 100% other cores are at around 4%; but i see 8 orange blocks updating the image (but over 1 core). blender is detecting the cores but not using them ??

Solved it wasnt related to blender, although i dont know what has caused this.
Windows has core affinity (taskmanger right click on process), but there blender was set to 1 core, weird.