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I did not know that. Is that because of a vent that feeds back into the fill tube?
No it happens when fuel gets into the EVAP vent hose. There is a valve which is supposed to prevent that from happening and as long as the valve is working you're okay. But if the valve fails or leaks then the fuel will fill the EVAP hose.
It can still happen with a working valve if you overfill it to the point you see fuel in the at the top of the filler neck. Some people like to do that. I don't believe it kills the canister instantly, but it shortens the life of it.