I've got the same problem on a Jetta, and it has nothing to do with the restrictor at the top of the neck since I've pulled that, and the problem has not changed.
There is something in the bottom of the fill tube causing the restriction that acts like a weighted gate, it only opens under certain conditions which is really annoying. I don't know yet what it looks like b/c I haven't gotten to take mine apart yet BUT on this road trip I have noticed that I have actually "lost" about 4 gallons of capacity b/c of this problem.
I cannot completely fill the tank b/c it stops several times (usually the first time after about 3 gallons) and there will actually be wet fuel sitting in the fuel neck, then it will suddenly burp BACK TOWARD ME and spill some of that - then it all drains into the tank. This is MOST annoying and wasteful! This happens at BOTH the car pumps and the truck pumps, it is NOT a flow issue. Something is wrong with the venting or the restriction in the tank, and likely the tank will have to be dropped to check this / replace with larger diameter vent tubing.