I can't confirm this, but I'm pretty sure this is what happened:
Runner on first. Batter has a .272 BA. Runner tries to steal 2nd, catcher botches the throw and the runner moves to 3rd. E2. But...
... my batter's BA ticks down to .271. I can only assume that the error was counted as an AB.
I went looking for the "Argue with the official scorer." but that feature has yet to be implemented.
Anyway, just wanted to put it out there in case someone else has a chance to notice it. (FYI: post-patch)
Thanks.