VirtualDub Audio Sync Issue?

[hech54]

I've been using VirtualDub MPEG2 1.6.11 for YEARS with no problems. I recently tried to fix a badly out of sync clip....and I messed with the settings so that MAY be the problem but...here goes:
Whether I use 44.1 or 48 PCM (wave) as the audio....as the video plays...the audio gets further and further out of sync with the video. As long as I press STOP...then play again anywhere in the "timeline"(?)....the audio will be in sync but then/again....it starts to go out of sync again and rather quickly.

I've been editing clips this way forever and all of a sudden I'm having sync issues....I don't get it.
My normal work flow is either ripping a chapter from a DVD. Demux it to video and AC3 audio(with MPEG-VCR). Convert the audio to wave with Ciler's AC3Tool. Load both and edit away....no problems.
I also copy a VOB from a DVD...then follow the same audio procedures...that worked perfectly too until now.
I also tend to run my material through FixVTS BEFORE I demux and convert to wave/pcm. I do that about 95% of the time.

I did it this way because I did not know how to install the AC3Decoder....but now I have that installed as well but I still migrate to my old tried and true(until recently) method. Could me installing the AC3Decoder have something to do with it or am I just reaching at straws here because I'm pretty sure I messed with that badly out of sync clip BEFORE I installed the AC3Decoder.
Did I tick a box or setting that may have caused this? I'm stumped...doesn't take much with editing software but hey....maybe you could shed some light?

Thanks for reading....

[Bjs]

"just reaching at straws here" .... yes .

Preview in vdub , any version , this happens , always has .

Use any other product to perform preview after clip has been realigned and saved out as a new avi from vdub only .

[hech54]

You could be right there. I just edited the portion(song) from the .VOB, with the wave audio and output it to a Divx file(experimenting with Divx) and it looks OK.