Mark -- Just reporting on a possible system bug.
A poster on GMF recently used the [relatively new] "Account Merge" function, with an owner email address as the "from" account. In so doing inadvertently left two of her groups without an owner. I know there is a safeguard to keep this from happening with the "Account Delete" function but it seems that this safeguard has not been carried over into merge.
I've suggested that she send you a separate note at support but I felt I would mention it here as well.