Reproduce:
Works as expected when Javascript is disabled.
I checked my scipts, but it's none of mine.
Can anyone reproduce it?
Tested with MW 1.25.2 in latest Chrome.
Yes, that was me. Can anyone reproduce it?
Anomie: I cannot provide the API query. It happens when you edit category pages. I don't know why the API bumps in, hence this ticket.
Prior to rMW536f98c, the API would set $wgTitle to "API" because various things would blow up without a title. But 1.25 includes that patch, so it wouldn't be using that title in general anymore. If you're going through action=parse and not specifying a title "API" is still used as the default there and can make its way into $wgTitle, so that could be it.
From the linked discussion, there doesn't seem to be anything to see here. Some script being used there presumably needs to be passing title to action=parse in addition to a text, but without more details we can only guess.