The gas is either leaking or vapor is coming out of vent hole. Is this normal?
Yes it is. Gasoline expands when it gets warm, just like anything else. If the gas was cool when you put it in it might expand enough to overflow. Just one more thing you have to be careful about on hot days.
In cars the gas used to get hot enough to vaporize and your car would die on the road until you cooled the fuel line somehow. It was called vapor lock. It took a very long time for makers to figure out how to avoid that.