Perhaps there is a pressurization issue, but from my limited knowledge, if it gurgles, there is an issue with the way it is filled.
My 3.1 ES gurgled (but did not leak) every time I tried filling it from the top cap, and the collector tank had a pretty good amount of juice in it. Once I started filling it upside down through the valve, no gurgling and the collector tank is dry.
If filling it from the top cap, I think it is not enough to close the air hole, the chimney's pipe needs to be plugged too. The reason I think this is because of this video. It is in German, but I think it is self-explanatory. Fast forward to 16 minutes 45 second to see how he fills the mini from the top.
I agree is seems to be a pressurization issue. I thought it was related to the o ring in the top cap but I looked at it closely and didn't seem to have any problems. I fill it with the plastic tips with the drip tip pointing down, and I do it slowly, so I dont think its a filling issue. At first i thought I may have been stuffing too much wick in there but today I'm using 1mm ekowool x2, with the tails not too long. The build looks textbook but still some leaking.
This thing has me stumped.