Well i use + - & < > In my song to change pitch and length and i alway make 3MLe to Optimize all the tracks
here the MML code of the song
It works fine in 3MLe (maybe not sound good cause i just organize tracks from midi not musician thoo)
but in mabi. It mess up around Meas 48 Like Melody line go a "r4." a head or something which is really weird