I still periodically get this problem using RealDrums. Which RealDrums set is it? Have you tried a different drum set? Does it happen to only one song? Also try a Return to Factory Settings.

Out of curiosity, turn on the Developer Mode in the RealDrums settings. That will generate a 'log' file of what is being generated. Once you Play the song, the log file will open and you can scroll down to the bottom to see if anything is being added to the end of the song. I suspect nothing will be found but you never know.

R