There might be a transaction rollback issue in the API. There was some small downtime around 19:07, 2 March 2012 (UTC). A user was trying to post a userwarning on a talk page [[:en:User talk:Kerev HaEmet]] using Twinkle. The downtime occurred, and after that the user leaving the message was greeted with:
The requested page or revision cannot be found
The database did not find a page or revision that it was expecting to find.
The relevant page of the wiki was "User talk:Kerev HaEmet" and the requested data (for error checking purposes) was: <didn't capture any more than this, sorry>
Which remained there. The page was later manually deleted, which solved the 'problem'.
Suspect that the API edit created the page, but failed to actually make the revision. This would mean that this transaction is not rolled back properly when a failure occurs somewhere between page create and revision create. Just a hunch of course.