This is my take on the situation. I could be way off base since I have not seen the gun and problem in person.
I don't think it has anything to do with the ammo or even the mag. I think the bolt is hanging on something in the trigger assembly. This could be happening due to the gun being in somewhat of a bind, perhaps from the stock being twisted slightly on the barrel. I have noticed upon field-stripping my mini, that there is some play. This usually results in the slide not sitting correctly in the gas block, but can also affect the slide and bolt alignment with the trigger assembly.
Try to correct this problem by:
1. Remove your magazine and check to make sure it is unloaded.
2. Manually press the slide lock and work the slide/bolt a few times to see if you can duplicate the problem. You might try rotating the gun in different ways to see if gravity will affect the action. (Try holding the gun with trigger facing up.)
3. Wether you can or cannot duplicate the problem, field strip your rifle and begin to reassemble it. Once you get your spring back in, work your action so you can visually see what is going on in there. Complete reassembly.
I am hoping that in this process you will notice your bolt getting hung somewhere. By simply stripping and reassembling your rifle, it should correct any "misallignment". But there again, I might be off base. But it never hurts to get a little more familiar with your gun.