It's not only the expansion that causes it, it's the pressure building in the tank if the cap is supposed to vent and doesn't. It will force the liquid out, if there is enough pressure.
Only if the liquid is at the level of the cap. In DADS50 post he stated the tank was only half full. The pressure can't push liquid out the filler cap when the liquid is over a foot below the filler cap.
It can and does.
I've had a similar thing happen with a different vehicle. The cap wasn't venting, and with the tank less than half full pressure built in the tank and fuel was pouring out of the vent. Once the pressure was released and the pressure dropped, the fuel eventually stopped coming out of the vent. Changing the cap to one that vents properly solved it.
I forgot what it's called, but when the pressure in a container containing both liquid and gas gets high enough, the gas will push the liquid out, which is what DADS50 and I have both experienced.
