Why does armor rating decrease when I enchant an item?

Why does the armor rating of my Dwarf Armor decrease when I enchant it?

It didn't happen when I enchanted the sword but strangely this happens when enchanting the dwarf armor and helm and probably for the gloves and boots aswell.

I just enchanted - Glass Armor (Epic) with Magicka Regen (25%)

Before the enchant it had: 134 armor After the enchant it had: 134 armor

While enchanting at the table, it had 90 armor. This seems to be a display bug with the enchanting menu.

I do have the glass smithing perk, I don't have the arcane blacksmithing perk

Its because you don't have the arcane enchanter perk.

Just tested it, with dragon armor. Legendary gauntlets started at 51 armor. When I enchanted it with a grand soul gem, the black star :), the base defense displayed as 26 on the enchanter. However when I checked the bow damage induced gauntlets in my inventory the armor was 51 again.

it is because you do not have the arcane smith perk under the smithing tree. need 60 smithing in order to purchase this one,