Haven't checked it, yet, but it sounds like a bug for which you should enter a Problem Report.
One minor point on terminology for the benefit of others reading this thread:
The pane in which the MIDI Chorus and Reverb controls appear is just the Track Inspector with no tab selected. Prochannel is a tab in the Track Inspector, and doesn't have anything to do with this issue.
EDIT, I verified X3 converted back and forth between the knobs in the Track Inspector and controller events in the file, while Platinum no longer does that.
Incidentally, the Ref. Guide for both versions says only:
"When loading a GM file, each track’s bank, patch, volume and pan parameters are lifted from the data stream and placed in SONAR’s Track view for you to see and edit on-screen."
I didn't find any reference to Chorus and Reverb events getting transferred to their respective track controls or vice versa, but that certainly would be expected.
post edited by brundlefly - 2016/06/24 16:13:00