Bop! I understand your concern very well! This **** is **** annoyn! It drove me

for month! I have now retried what you were sayin and i m most times usin the effects at my rack anyway and in my case it works fine now!
I don’t use program changes either! … and exactly therefore: switch the **** pgm change off! You don’t need it! especially hit the window button on prg change field at track field and set parameter transmit pgm change in this track = no! even if it may not solve your prob it doesn't hurt you! (I did it now on all tracks! … and set it to autoload! you can always switch it back on once you need it!)
Further: try to switch all unneeded midi **** off! On the mpc as well as on your rack module! For example on my unit (virus b) on the virus all pgm changes, multi pgm changes are switched off!
What I also did (maybe this is a cause of your prob): I disconnect midi cables if not neeced! before I always had midi out mpc connected to midi in virus! And vice versa to record cc messages on the mpc! Try to disconnect the midi out of your rack to your midi in at the mpc (to avoid to send unneeded midi messages from your rack to the mpc and back to your rack again!) And just connect it if your recordin cc messages!
Hope you get your things together! Good luck!
alto