It could also be them trying a new playstyle. My friends and I tried going to the Lighthouse twice just playing fair, no cheap weapons. 2 times we made it 8-0 and lost on round 9. We finally snapped and used all 3 thorn and got the the lighthouse twice in one night, both on the first try. Switching back to not being a Thorn -blam!- is a rough transition, which could explain their troubles.