I never "burn on the fly". It prevents so many errors and mistakes. I always copy the disc contents to the HD using
Anydvd and DVDdecrypter. I then run my compression program of choice (
Clonedvd,
dvd2one, recode) against those files. I then load the resulting files into
Powerdvd and check them. If all is well, I burn with Imgburn or
Nero.
No coasters, no mistakes.
But yes, if in doubt, load the disc in a dvd player and see what the extra audio/sub tracks are.