Originally, this item was one of the possible rewards for an Alliance-only, Mage-only quest. Astral Knot Blouse, along with Astral Knot Robe, were removed from the game when class quests were deprecated in Cataclysm.
It's a shame because Astral Knot Blouse had a rather uncommon model. "Blouse" is something of a misnomer because there are two parts to it - a vest plus a skirt. It's a robe without the typical shoulder-to-wrist sleeves.
Currently, the item has a display bug that was first spotted in Patch 4.3.0 according to a Wowhead comment. I was browsing through items using WoW Model Viewer and noticed the bug - it's what brought me here, actually, because it is very atypical for a named, non-template item in game files to have an incomplete texture. (The bottom portion of the model simply projects the texture underneath, whether it's pants, skin, etc.)