So, here's the problem.
Zedd/Rita pick a townie to be a monster. The spell succeeds. The Townie, however, fails to submit a weakness and contacts other townies (and, ideally, another Ranger) to let them know they've been put under a spell. Since the monster didn't submit a weakness, they can't make a hit overnight. If they've managed to contact a Ranger, then they can be "saved". Repeat this over and over and you've got no Monsters and no hits from Zedd/Rita - and the townies can slowly vote out people until they manage to get Zedd and Rita.
After talking things over with Zedd, Rita and Zordon, here's the fix we've came up with that doesn't over-power one side while giving both sides the chance to win.
The fix - If a Ranger saves a monster, that townie then has a 90% chance of "leaving town" - thus being kicked out of the game. Granted, the Townie-monsters could still contact other townies, get saved and slowly make it an automatic win for the townies, but those monsters will, very, very likely, not survive the game (i.e.: they'll lose).