never heard that one before, was it fitted properly, sounds like a leak to me 
I have heard of it before in the US, but cant fort he life of me remember what the problem was. I suggest anyone having this problem searches here and my350z for the answer. It shouldnt happen, but as I say, I have heard of it before. 
  
It happened to me on my old car so it is a true statement   Fletch fitted mine too so I'm pretty sure it was installed correctly