This came up once on the ML: If an exception is thrown when initializing a lazy val, the val is null; but you can attempt to init again and it can work magically. (That is, the "initialized" bit flag for the lazy val is not set on the first failed attempt to initialize.)
I think the case on the ML had to do with init order of vals in traits, so maybe that's your problem. It's infamously dangerous to rely on it, hence the advice to use defs in traits. See Luigi's comment on DelayedInit.