I don't know if this is a JABB issue or a SONAR 5 issue, but I've never seen this in SONAR with GPO (or anything else, for that matter).
I've got a piece which sounds fine if I play it from the beginning, but if I start playback in the middle, suddenly everything's out of tune. If I pull up the first JABB player, I can see the pitch wheel drop as soon as I start playback, even after I've gone through and deleted all the pitch wheel events in the project (the event list has none in it, and when I export to MIDI and reopen it, there are none in there either).
However, when I'm in the piano roll, the event view selector does show pitch wheel events in the dropdown list of available event types, and it's only supposed to display the events that are actually present on the track. Yet when I deselect everything except the wheel events, no events are visible.
If I put a pitch wheel event at the beginning of a MIDI clip so it's in tune, it plays properly -- but if I start playback after that event, it goes out of tune again.
Any idea what could be causing this? The weird thing is, it's only happening to one of the three instances of GPO I have in the project -- the others stay in tune. It's most vexing.