I have a .sub file demuxed from an OGM file. When I import it into DVD-Lab pro's subtitle thingy, it generates a substream without errors. When i compile the DVD, there's at least one spot where the subtitles don't appear. I've checked the .sub file and it seems all right. The subtitles for the timecode where they are missing are in the sub file, and in the pre-rendered part of DVD-lab pro (before it generates an sp1 stream).

EDIT: The problem seems to be eliminated when I use non-drop frame (30 fps) instead of drop frame (29.97). However, this makes all the subtitles appear a split second later than they should.

EDIT EDIT: I think I've found the problem, the subtitles were timed for the original frame rate of 23.97, and the video was re-encoded for 29.97. I used Subtitle Workshop to convert the subtitles to 29.97 and they all show up fine now.