I applied an RPU on LAX-DEN-PTY for my wife. A few days ago, she got an email notifying her about reservation change to LAX-IAH-PTY and she accepted it. The reservation now shows LAX-IAH-PTY, with only IAH-PTY shown upgrade requested. It also shows that she is waitlisted (for R) on LAX-DEN-IAH.

Is this common? Why she is not waitlisted on LAX-IAH?