Good Thread! Some Things I noticed:
I. Playing back OS1 Projects on OS2:- Everything probably sounds different: because the Filter was changed, Filter 2 removed, and also Sample Layer 4 was removed. So if you did a lot of filtering and used 4 layers, you lose a lot of the original sound. Also the Mixer setup was changed, so there also might be differences in volume
II. Playing back OS2 Projects on OS1:- All Samples are cut off when playing back as if they were recoded in note-on mode, when they originally were recorded as one-shots. Could be a result of the ADSR addition in OS2.