If Leoben - for whatever reason - believes that Kara can't resurrect, then it means whatever is in front of him isn't Kara Thrace, which is why he's scared. Which may seem obvious but really only half occured to me as I just figure...in a show that's all about how memories and behaviour are more important than biology, of course she's Kara, the question is - how is she alive again?

I'm going to get my podcast write up posted by tomorrow and Ron covers why Leoben reacted as he did. It does have to do with Leoben's faith and his beliefs being thrown into question. And the Kara Thrace in front of him not being the Kara Thrace of his visions and the person he professes to love, well, it's all too much for him to handle. Now the question is, does he keep what he knows to himself or does he share it with the other Cylons?