If you do ask him, be sure to post here about it, I would definitely be interested in what he has to say.
About the question at hand, Im not really sure what could be wrong, but just to be on the safe side, fill it up with gas and listen for a leak of some kind. Thats a pretty obvious thing, but it wouldnt hurt to try. Also try another M9 magazine in your gun (obviously one that is working and in good condition) and see if you get the same effect. If that doesnt work it may just be that the slide is too heavy and that there is nothing wrong with the gun, its just that the slide is too heavy. These are just common sense things you may want to try. I dont have much experience with gbb's, so Im just trying to think of the more generic things that might fix it. Again, good luck and be sure to let us know what happens!
-Scott Keefer