IMO it's a leaking or misplaced O-ring. The two times this happened to me with my Kayfun clone it was the small O-ring in the center of the top part of the device:
That O-ring would fall out of its place and into the tank when I put it together. I unscrewed the drip tip and used a small screw driver to keep it from escaping during assembly. I have not had this problem again.
Now, it could also be one of the other O-rings. Any one of them out of place or simply not sealing for any reason can cause this to happen.
Hope this helps.