I love these kind of answers.
No it is NOT fixed in 1014 as I have several servers running that that NOW can't create email addresses.
I hate this control panel and have managed to remove it from most but daily I have to put up with new bugs that didn't exist before.
It's either the magic 'error 500' that appears, then you upgrade, then you jump through all the hoops and pray, then on some you end up reinstalling. Or it's the random plugin failures. Now not being able to create email addresses.
So you come here to find the answer and you inevitably see NO explanation of the solution just 'fixed in [insert version]' which it usually isn't.
So if anyone can add something useful to people who are running the version it's supposedly 'fixed' in - do let us know.