That's just your rank being updated (recalculated) from your previous session.
The rank itself is only updated once a user submits a score, else only in intervals going out from #1 to the "last place" (user with the lowest pp count).
(I don't know the interval, but I think it's every 24 hours)
So, seeing some rank changes after submitting a score is normal, can also happen mid session if you go AFK for a couple minutes, or after playing a longer map.
