I had my master keyboard of 22 years (Korg SG1) die on me recently.  I have several keyboards just collecting dust so I swapped out a Kurtzweil SP88...it worked fine , but I don't like it's action.  So I swapped out a Yamaha S80...I really like the action,  but the midi output seems to go buggy.  Some notes don't get sent,  some crazy notes get recorded and stay on,  many times the 1st time I play a note while recording midi every midi instrument sounds (It will scare the heck out of you). Put the Kurtzweil back in and everything behaves well.
 
Is it normal for the yamaha s80 to act so crazy?  is there a fix of some sort?
 
Thanks!     

I never played an S80 but I don't think they would have sold very well if that problem would have been wide spread . This leads me to think that there might be a problem elsewhere. Bad midi cables, a sticking or hanging foot pedal, or an incompatible foot pedal....or worse...something is bad inside the S80.
 
Just recently there was a thread here on a glitch in Sonar that causes some midi notes to hold for too long...they have a fix for it.A CAL script.