Has anyone messed about with candles yet in Luxrender?

I am having some issues since the one I am using has a transmapped flame.  The moment I put up the ambient to make it an emitter the whole flame material area is visible in Lux not just the area that should be because of the transmap.

Likely I am just having a brain dead moment and missing the obvious, but if anyone has a clue, it would be appreciated.

Or is it that transmapped objects can't be made into emitters?