I saw the new Bardiche and thinking, that be a great new weapon for my Wrathguard then it auto learned the appearance when I purchased it on my Warlock I wanted the actual item to sit in my bags so my summoned pet could use it, not automatically added to my collection.
It’s hard enough to collect two-handed melee weapons as a warlock when most are locked behind personal loot, never showing up. In those rare cases I can actually purchase something I get denied again forcing to be auto-collected.
All these transmog items from the Post should produce items in your bag, that you have to right click to add to your appearances. OP’s problem is precisely why this should be.