This may or may not help. On my XP50 and XP60, sometimes when you stop a song midway, the controllers on the unit are left at a stand still and need to be reset.
When the controllers are left at a stand still, there will be some unexpected vibrato and aftertouch left on some parts and some tones may play a half step up if pitch bend data has been left hanging.
On the XP, all we have to do is press [Shift] and [Undo] and the MIDI controllers will reset themselves. I'm not sure if this works the same on your unit. Look in your manual.
If worst comes to worst, I would highly recommend that you get a memory card or a computer program that would allow you to store your stuff somewhere. You would need this despite your problem. Then do and entire reset.
The Infamous EPU.