There's no need to send the content to the server, a clientwise js check would be much quicker.
We could for example reuse the jquery ui to display a simple alert, and if the user dismisses it, but clicks save again, then save it.
I'll write up a short js function soon.
Version: unspecified
Severity: enhancement
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=18052