Help needed with tank fill problem.

I posted this question in the tanks thread as well. But I guess it belongs in either. Just trying to get as much input as possible. Thanks. 

If anyone has a clue as to what is going on here, it'f frustrating me. 

So I'm filling a Compatto from a 4500 psi 75 cu Ft tank. The tank reaches under 3000 psi, and I figure I can still get a few fills out of it, so I fill the gun, but when I try to bleed the line, the valve in the gun doesn't close and basically will not stop "bleeding" until the gun is empty. So the only thing I can do is shoot tethered and then bleed the cylinder dry. Is this normal? Is there something wrong with my gun? Do other PCPs behave this way? 

Thank you...
 
"AirSupply"Sometimes a small piece of dust or something will lodge and stop the valve closing as it should. You could try a short sharp burst of air when filling instead of slowly just to try and dislodge anything that could be in the valve. 
Michael
Will try this when I get my tank filled again. Waiting on an AV booster Thursday or Friday. 
 
May be an issue as stated above, but i have never experienced anything like that. For several years i only had two scuba tanks and while i only filled my two Marauders to 2400 psi i would keep filling the guns even when i only had about 2100 or 2200 psi in the tanks and never had an issue as you described.

Could it be the check valve in the gun is not closing because of how it is set, too high?