Gas leak, how could this happen?

So I went for a 50 mile drive home yesterday. Needed gas so I stopped off in my town (after the 50 mile drive).

When I pulled in a guy came up to me and said there was gas leaking out of the back, especially when I took a turn.

So I look and sure enough the tank is all wet/dripping gas. So I filled it up, it needed 10 gallons, and the leak stopped. Drove it to my garage, all the lines to the filter were fine so I'm guessing it was coming from the top of the tank? Pump lines?

Just weird since the problem only existed when I was very low on gas and went away when I filled up.....

Yeah its very strange, I just dont get it. I did take the tank out of the car to put in a new fuel pump. It was leaking alot, not just a drip, made a nice puddle very quickly at the gas station. So weird though, I filled it up and it wasnt leaking anymore, drove it home and it was all dry. I jacked it up from ther rear and started the car and it wasnt leaking anymore at all....