We had this exact same thing in a game last year. The score was 36-0 late in the 4th quarter in a pop warner 14 year olds game. We discussed it and just called it a failed try instead of spending all this time talking to coaches and having them think we're idiots.
On a varsity game, or in a close game, we'd have to give the offense 1 point.
When we saw this play, it seems like it would happen more often. Running back rolls out to one side, fumbles, ball is not really moving any direction, defense in attempting to recover ball squirts it back into their own end zone where they fall on it.