I am using Sony Vegas Movie Studio HD Platinum 10, but I had a similar issue with version 9 (same product). I have a recurring project, where I add about 4-20 short (2-3 second) video clips to a project (the clips are 800x600, avi). I have preferences set to automatically place the video clips in order, without overlapping (no Auto Crossfade).
The problem is when I render - I usually render to WMV 3mbps (640x480). After a few frames, the render will 'pause' for a second or two, and my computer fan (this happens on core i7 desktop & core i7 laptop - both 8GB ram) will whir up, then the render will complete. But when I view the rendered video (Windows media player, or other), there is almost ALWAYS a brief flicker/blank screen between clips 1 and 2. No other flicker generally occurs between other clips.
When I preview the video in Vegas, it does not usually show this flicker. When I super zoom into the timeline, there is generally a very small, fraction of a second (<1 frame) gap between the video clips (but this is on all clips, and the flicker only occurs between clip 1 and 2).
I suspect this has something to do with the computer 'revving up' to do the render, creating a blank frame between clips, but I can't seem to figure out how to fix this. Any ideas??