That is accually kind of common with sleived flutes, although not usually after six months. The wood wants to move with temp. and moisture changes, and the brass weon't let it. Though I must admit I've only seen this on older instruments(50-60 years old). The crack can be filled and the surface sanded, although based on the value of the instrument that might be better off done by a proffessional. I don't know were you're located, but in the Northeast (USA) Skip Healy does that kind of work in addition to building fine instruments.