I'm having this problem in 9c where I lose the trimming preview on the timeline. (Trimming a clip on the timeline and see it trimmed on the preview monitor)
I've reset 9c twice already by the ctrl & shift method. 8c works fine and has since its release. Any ideas?
It's a tough one (for me anyway) to explain, but here goes....
Place a clip on the timeline... grab an edge and trim. Normally I can see the clip updating on the preview window. After a few days the trimming/updating of the clip disappears on 9c until I reset it (ctrl & shift while loading).