I know that I am a little late to this thread, but this was something that concerned me too when I first got my first SuperNova... having been used to the Rem. 870, where the elevator is basically just always springing down, I thought it was weird that when I put the first shell into the mag, the elevator stayed open, and then came down after I pumped it. I now understand that this is perfectly normal, some mossbergs do the same thing... and you may find out, in a tactical situation, and with an extended magazine, when you need to reload a lot of shells fast, this makes it a million times better, then fighting the elevator spring every shell you put in.
I'm such a fan of the SN, that I use one bird hunting, and I have a tactical one for my duty shotgun!!!