I have SonicFoundry Vegas 4.0d on Windows XP Home using a webcam (why not) to make shrot clips.
The video is all messy when I play a video track. The "mess" stops after 4 or 5 seconds of video playback. And this is not all. When I render that video it is still messy. Looks like it's a very ugly bug in Vegas.
This can be solved by adding the first 4-5 seconds a generated effect... or just black.
I repeat, this is one ugly bug that the SonicFoundry company have to work it out.