Is it losing sync or is it not?
 

I have large VHS conversions of non-HD footage that I'm using in a project. Large because each file is 2 hours of footage.

Whenever I load one of the 'tapes' into Vegas it loses audio sync by a number of seconds.

When I cut and copy+paste portions of the tape into another Vegas project, the sync is still lost.

When I render the original whole project though, the sync is fine. When I render the new project with copy+paste cuts, however, the sync appears to be lost.

What the heck is happening? Why the apparent sync loss, and why does the loss carry over but render fine.

Also, pre-render appears to have no affect on the preview-sync-loss.
-Adjul

Re: Is it losing sync or is it not?
 

I'm afraid I can't answer your question but I can report a similar situation and how I resolved it.

I have been editing some event footage shot on Panasonic AF101s and recorded to a Samurai Blade in the highest quality DNxHD format.

My edit system is pretty highly specced and I was able to apply colour correction and preview it very smoothly. I had recorded audio separately on a Zoom H6 connected to the mixing desk and I synced it all up nicely (muting the original audio from the camera) - or so I thought. Although everything looked good in preview (and it was completely smooth - no judders whatsoever) when I came to render the audio was several frames out. By zooming in on the timeline and closely examining the audio waveforms for the Zoom and camera audio tracks I could see the offset quite clearly (before anyone wisely suggests PluralEyes, I do own it, but it does not work with DNxHD).

The simple solution was to disable the colour correction plugins, then sync the audio, then enable them again and render.

So, even though my pc appeared capable of smoothly playing back heavyweight footage with cc in real time, in fact the video was lagging behind other tracks.

I'm guessing your audio is embedded in the footage so my experience probably won't help you but I thought it might be useful for anyone reading this who is trying to troubleshoot their own audio sync issues.

Re: Is it losing sync or is it not?
 

I had the same issue a while back in Vegas 9. I never did figure out why it was happening, but the render was fine. I was doing the same thing you are. I was converting some old VHS tapes. I had other issues that turning off "Quantize to Frames" solved. That was just a small sync issue though.