johan_80: I'm seeing that problem too, although I hadn't realized that it had something to do with RR changing. For me, when I start a video it sometimes plays normally, then when I fast forward it goes into this extremely stuttery mode (more of a slide show than a video).
A dirty workaround/fix is to minimize MediaPortal and interact with a window (just fire up explorer or anything) and then go back to MediaPortal. Now the playback is perfect!
I hope this can be solved now with the ability to communicate with the presenter.