Stange sync error with Nero

Hi all,
I am using the latest version of Nero and have noticed a strange sync problem with DVD’s I have burnt. They begin ok but then the audio sync creates ‘lag’, strange but not unknown, right. But when I ‘rewind’ or go back via my stand alone dvd player whala it works again. I burn with a Plextor 708a (rev 1.07) and my DVD palyer is a Denver DVD 141. I experience no other problems when playing regular store bought DVD’s. If it was a software issue the sync would stay out of sync, right? So it must be the Denver?
Not a big problem, but I would welcome any suggestions.