Filling Up Gas Tank?

Ok so, I dont know what causes it but sometimes when I go to fill up I cant press full power on the gas nozzel cause then it just stops like it would if the tank was full, except I fill up at like quarter or half (mostly quarter but if i have to stop at a gas station to get a monster for workout or something) so does anyone else get this? I jsut had the problem where if i move it around in different variations of power (power = how much the handle is pulled down to let the gas out) or depending on how far in I put the nozzel or how much i pull the nozel out, most of the time it'll stil stop when i push full power, a few exceptions when i pushed the gas nozzel all the way in and hit full power it was fine.. its annoying!