If you used the "Erase All" rather than erase each program individually (and maybe missed one) then this should not have happened. If it did happen with "Erase All" then that's pretty strange and I would question the integrity of the source DVD-RAM disc or perhaps it was an incomplete trim (shorten segment) occurrence. I usally use Erase All rather than Format except on my old E20 which doesn't have the Erase All option and have never had a problem with snippets of old programs rising from the grave, so to speak.
Vic