I too have had this problem and have had it at the dealer 3 times now for the same problem. First time they said the "Heavy Breather" was loose, so they changed the gaskets retorqued everything and sent me on my way. The second time I brought it back they checked the gas lines, vent lines, retorqued everthing (again) and replaced the gas cap. The third time I took it in they checked everything all over again and said...you ready for this? "These bikes just do this for some reason if it persists don't worry we added it to your bike history so we will warrenty it even when warrenty runs out."
I myself am baffled over this and at this point the only thing I can do is leave the garge door open for about twenty minutes after I get home with the fan running. By the way my bike is an 09 Electra Glide. The Misses 2011 Hertiage never does this.