Fred,
I just opened a old project that had a whopping 26 subtitle tracks. They all show up correct, even on a DVD player.
I too use a semi-transparent black background. The size gets automatically corrected by height but not by width.
About 4 years ago when we got into subtitles we tried Adobe products (and a few others) DVDA beat them all hands down. I wonder what the score would be today?
I wish I could help you.
Sorry,
Jeff
http://www.narrowroadmedia.com