While perusing the MB forums, there were several discussions of over-filling when getting gas. It seems that if you keep pumping to get it as full as possible, the excess saturates the evaporative canister, which triggers these types of things. According to them, it has even kept the vehicle from starting and running, or not running very well. It takes it some time to correct itself and dry the canister. It is a known problem with the MB group.

I don't know if that is what is happening here, or if it even applies, but may be something to consider the next time you fill up. And I always make sure the cap clicks two or three times when putting it back on. Just something else to consider as a possibility.