TS100 behaving weird in power monitor

[Curious2know]

Hi,

so I've flashed Ralim firmware on my TS100 today and I wanted to test how much power it draws when doing the wet sponge test. I got one of these wallplug power monitors where I plugged my 24V PSU in. When heating up to 320°C for the first time I can see the iron draws up to 80 Watt. Now when I put the tip in a wet sponge and I can see the temperature dropping slightly on the display of the iron, the power draw jumps to 0W. As soon as it reaches 320°C again, the power monitor shows values between 5W and 10W.
Can someone explain why it jumps to 0W?