If your heater accidentally fills with fuel with the flame off, you can create the potential for a real problem. If you try to act smart and throw a flaming paper into the fuel to act as a wick, you will be sorely punished by an out of control blaze until the fuel burns off. Instead of dealing with such a massive fire inside the heater, the alternative is soak up the fuel with a toilet paper roll and then continue to use as normal.
In five years, this is the first time I have had an issue with accidentally opening the fuel valve without knowing. Fuel flowed into the heater for a full day before I noticed the small puddle of fuel on the floor below the heater. This situation was easily remedied though, allowing me to continue using the heater without any issue.