The accounts tab on the SE user page operates on a ~1-day delay, and since you passed the 200-rep threshold during the past day, it hasn't been updated to include your MSO account yet.
When you click "show accounts with less than 200 reputation", the entire page is updated to show the up-to-the-second status of all your accounts, which is causing your MSO account to suddenly appear with >200 rep. I agree that this behavior is slightly confusing -- we'll be rolling out a backend overhaul of the SE user page in a couple weeks, which will greatly reduce the delay and eliminate the inconsistency between before/after clicking "show accounts...".