My guess it that the problem lies in the sequence, since it only occurs on certain songs. Some files will read differently on different midi playback devices, hardware or software.

How were the sequences created? Do you have a software program that provides a comprehensive analysis of all events. Have all tracks been rechanneled? Since tracks are affected other than those you're tweeking, there may be some channel event crossover. Look over the events list very carefully. Good luck.

Glenn