MPEG2: Audio - Video desync after 30 min.

[Gic]

I recently started to use BSPlayer for MPEG2 videos because of a very nice feature: custom aspect ratios (anyone who wants to output correctly to a PAL TV knows what I mean - must use a 5:4 aspect ratio).
Previously I used it only for DivX movies.
I used various MPEG2 decoders. The default on my system was a Ligos MPEG2 decoder and it didn't corectly resize the image. Then I used a Roxio MPEG2 decoder and it worked OK. Also I tested a MainConcept decoder and I noticed a little image cropping.
But the main issue is the following:
After 29~30 minutes of playing, the audio goes ahead of video for around 1 second or more. If I stop the movie then rewind and then jump to the 00:30:00 time the video is back on sync. After other 30 minutes more the problem is back. And it's not a decoder issue because it manifests always with any decoder.
The MPEG2 files are created with Intervideo WinDVR 2.0 or ULEAD VideoStudio 7.0 and are playing correctly with MediaPlayer, WinDVD etc.
Regards,
Gic

[Gic]

I'm starting to suspect that VideoStudio is making some shifts during final rendering. I will test with a non-edited MPEG2 file and let know the results.

[Gic]

Yes, it seems VideoStudio is guilty. A whole captured MPEGII is playing fine, but after cutting some scenes the edited video manifests in that way.
I still don't know why after jumping to 30:00 the video is back in sync.