I know the original post some time ago but ....
Yes - we have had this in the UK (Mondeo). The filler pipe to tank connection leaks when the tank is under pressure after a drive and the tank if over 1/2 full. As is gets worse, it will leak even with the tank on low. It's bad in hot weather after a long drive. If you release the pressure by opening the filler cap, the leak will stop. As a temp fix - leave the filler cap slightly loose until you can get the seal/gasket replaced.
I think the tank is pressurised maybe to slow evaporation of the fuel - anti-pollution.
