Well, if I read you correct, you did not put the bouns item on "before" you improve the armor. You don't get to improve it more/again after you've already improved it, even if you find an item/potion that gives you a bouns to do so later.
No sorry, I went to the table without the magic gloves equipped and clicked on the armor to see what the improvement would be, it went from 46 to 55 rating. I cancelled it, went and bought the moonstone, then put on the gloves and did it, still only came to 55. So yes, I was wearing the smithing gloves when I improved the armor on the bench.