Originally Posted by
eng3
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I just seem to remember one time in the past, doing this and it actually splitting, causing issues with the other pax trying to check a bag. I distinctly remember that no one got upgraded though. This was a while ago though, perhaps back in the auto-checkin era.
As others have mentioned,sometime back (over a year ago), UA changed the process and the splitting will occur on if needed to actually partially upgrade some.