Do you have more than one magaizne?

If so, does this happen with both magazines?

When you insert the magazine, do you hear a "click" when it is fully inserted?

When the magazine is fully inserted, is it able to be removed without hitting the button?

Are you right or left handed?

If left handed are you somehow hitting the mag release with your hand?

If right handed, and shooting wiht both hands is your left hand making contact with the mag release?
-> Try shooting right hand only.

Your Bersa should have come with two mags .......as above try both....if problem persists have a friend shoot it and see if they have same results...shoot pistol carefully avoiding the mag release button.......JJ