Sometimes a module will have a star requirement that is more or less than the total it is possible to earn; Is this intentional? I'm talking about modules without victory tiles. For example, Heart of the Black Forest encounter 3 only requires 3 stars to complete even though there are 5 enemies. I've even found a module that takes more stars than it's possible to earn, but it auto completes once the last foe falls anyways. (I forget which one; it involved Kobolds and a little maze. I think it was pretty early on)
http://www.cardhunter.com/forum/threads/more-stars-showed-than-required-to-win-a-battle-minor.1024/ It was discussed as a possible design decision, but likely just oversights from the rebalance pass (removing/adding enemies and forgetting to chang win conditions).
It's entirely possible for a battle to have less stars require to win than the number of enemies. For example, the Woodhome Walls battle is designed that way. However, if there's not a clear reason why it looks like that should be the case, it's probably a screw-up on our part.