I have the same issue. After rendering with my Vegas 9 pro (ver. 9.0e) it is impossible to play with any player. I have a media center Ultio MVIX that virtually plays any format. It plays M2TS file but it’s very choppy.
So, I render into M2T format and after that I convert the file into M2TS with 4UM2TS converter.
If you found the way how to fix it, let me know.
Sincerely,