Doctor M said:

Just an update, the BDSup2Sub jittering issue may only be apparent if you play back on a 480i device. (Not many people have noticed it.)

Someone new has taken up development of the software and has stated that he will take a look at the issue in the future, so I can't see making a modification to the guide at this point.

If anyone does have an issue with subtitles displaying badly with the guide as it currently is, PM me and I'll post the old (longer) method as a stop gap.

Was this issue ever fixed? I rely on BDSup2Sub pretty heavily in my project and want to make sure it's not affected.