KJW USP Slide Issue?

[Turd]

I do not have enough experience with GBB's to decide if this is something legitimately wrong with the gun. I have a KJW USP and what happens is when I charge it up with propane and use it, the slide will lock back even when there are clearly still rounds in the magazine.

My first guesses were these:
Not enough gas in the mag? (but when I open the valve a decent amount comes out).
The mechanism that holds the slide back is a little over-zealous?

And another minor suspected issue: the safety does not SEEM to function. Is the safety on a USP supposed to disable the trigger or what? Because I can still pull the trigger and fire. Any ideas?

Oh and is it normal that when reloading, putting a new mag in will AUTOMATICALLY send the slide forward to chamber a new round? I thought I would have to release the slide lock every time?

Any tips or suggestions would be grrrrrreat