After examining the black video output issue, it's not the zeranoe build all alone. It was a rather complex situation in my project file, directly accessing the audio track of avi-files. I don't think it's worth to be explained detail.
From my experience you can safely use zeranoe's build with video files in quicktime motion jpeg format. Sorry for shooting out too fast on this one
Apart from that, it seems to be reproduceable that reaper while starting playback shows one frame before the actual starting point. I'm gonna post some info on that in "v4.10rc2 - September 23 2011".