Guild Wars 2

Amulets, Rings, and Accessories. These are the only 3 types of items that can’t be placed in Transmutation Stones.

Thats not a bug. First off all cause transmutation stones, are designed to work on weapons and armor only. The second reason is that jewelry like that isn’t visable on the character (backbraces can be visable when it is the guild’s back armor andaquabreather is visable underwater) so there is no reason to being able to transmutate them. If you wish to move an upgrade from one piece to the other you can use a black lion salvage kit.

No, backbraces are not visible, even if you take off all of your gear.

Single-use. Combine the appearance of one item with the attributes of another. Items must be of the same type. Usable on all item levels.

Nothing in there says it can’t be used on trinkets.

Some backbraces are visable e.g. the guild back pack and the engineer starter backpack. Engineers who like the starterbackpack can use a stone to keep a visable backbrace when they got the story reward one, so there is actual use. Again there is no reason to transmutate jewels. The word ’ items’ in the description is so widerange you can’t call it a bug cause of the term (you can’t transmutate things like gold ore, while it is still an item)

Jewlery can be visible. Platinum MF masterwork set is visible on my asuran.

While minute it is visible.