Just out of curiosity, since I don't fly the 172: Do you also select either left or right when refueling, or do you leave the selector on both?
I fly a 182 and always try to remember switching to L or R when refuelling for precisely that reason.
However there is a quirk in the 182 fuel system whereby it only vents on one side and then is a vent connection between each wing. When the tanks are fuelled to full then there is a tendency for fuel to flow through this as well.