My SuperNova does something similiar but it was designed that way.
I'm not sure about the Remy. When you shoot the SuperNova it will disengage the slide like that just so that it is easier to move. Having said that, I've not noticed mine having that much movement, it just sort of releases the slide more than anything else.
Wish I had a better answer for you but I'm no shotgun guru. Hope they get it fixed for you.