Keep forgetting about the plugin.
The 'weighting' task mgr has does act strange sometimes but having a high cpu load w/r4.exe is normal and it usually takes all it can get. However it is strange that your load increases, especially so much. You would think the opposite since the 'in focus or visable' thread would get more time slices. Checking this as I type and and it either decreases or stays about the same between visable/minimized. In focus doesnt seem to matter.
I Have all AMD's here so cant check HT, wonder if its a oddity for some reason due to it. For curiousity did you bother to try it w/o HT enabled to see what happens?