I'm not sure how or why, but it does. I think it has to do with how Womble sometimes thinks extra frames are supposed to go in due to the 24->30 fps conversion. It's why I always demux, note problems like that, and create a separate audio mix that accounts for such glitches when they appear.

I also do not use Womble to author DVDs. Only to splice video and a corresponding audio reference file. Womble for video, Vegas for Audio, DVDLab Pro for authoring. It's been near-perfect for me every time.