OK...I was editing in PRV in Platinum today. It happened again, except I deleted a pitch bend CC I had drawn in the controller pane...and a note disappeared in the PRV.
IF a note is highlighted in the PRV....any note....it will be deleted if you delete any CC info in the controller pane...regardless if the note is associated with the CC you are deleting. You have to make sure no notes are highlighted before you delete CC info.
I draw CC information in the controller pane all the time, and delete some too...and never experienced this in X3. Will have to try it in X3 tomorrow and make sure.