Issue #1: I have only seen this with missing items in a set. When trying to identify a missing piece of a set, it is showing an unrelated item.

In my case: Siegebreaker Battlegear (Recolor)
Body: Longbow of Trials
Hands: Oronaar Miner's Pickaxe
Legs/Feet: Showing properly

Darkruned Plate (Recolor)
Shoulders: Gorestrung Longbow of Kel'tann

Issue #2: Showing obtained sets as greyed out and unobtainable: Wendigo Woolies and Celestial Observer's Ensembe