I'm having the exact same problem.
The 46second video was recorded on a DXG camcorder. In the avi trimmer, the Video codec is H264, audio codec is unknown.
Looking at the codec information in VLC, the codec information is:
Video: H264 - MPEG-4 AVC (part 10)(H264), 1280x720, 29.970029 fps
Audio: MS ADPCM audio (ms), Mono, 44100kHz, 16bps.
If I start the trim after 300ms, then there's only solid gray for the rest of the video. I do this with only the video stream selected in the avi trimmer.
Any hints? Send me an email for ftp login and password if you need the video (it's 54 megs).