If everything is clean and there is nothing causing it other than it not be "true", I would call the manufacturer. I have never heard of this and it would frustrate the hell out of me.
2013 Stumps Classic - Delivered 4/15/13
Large BGE - Rescued 2012
2010 WSM 22.5"
2010 Weber genesis gas grill
Rescued 22.5 Weber One-touch gold
BBQ Guru CyberQ
2011 Built UDS - Retired