I have that does the same thing. It's a SPAD so I can see the tank all the time. I have not been able to find the problem. I did find a cure. I just leave about 1/4 throttle in it at the top before I jam the sticks. The extra exhaust pressure seems to do the trick. I read a neat idea on another post yesterday. They suggested putting a one way valve in the pressure line to keep tank pressure up. I've got to try that. In theory it should cure this problem and maybe even help throttle response in a hover.

David