I’ve experienced this now twice on separate occasions:
If I’m applying color information during the Sync process by quickly using the 8 or 9 keys, and one of the shots I cycle “over” as I’m counting back to the appropriate camera happens to have framing set (flip H / flip V) - I see it flip my image obviously till I hit 8 again to attach the correct color - and even though the image is correct on screen, the rendered MXF is flipped. If I check the clip again in bin or the reel, it looks correct. If I send the clip to a new reel, it’s now corrected.