I had the same problem, but was my fault.
DeVeDe displays original frame rate. For instance, it was 24FPS and I created the DVD using PAL/N. With PAL/N the "final" FPS was 25. I didn't note that and I burn the DVD. Obviously, subtitles will be out of sync, as the correct subtitles were for 24 FPS.
I re-created the project, and I set NTSC instead of PAL/N and the *final* FPS were 24, the same as the original .mp4 file. You should take note on all this stuff, the *original* length, the *final* length and the FPS. They SHOULD match in order to have subtitles properly sync'ed.
Regards,