The behavior of the quest-rewarded item Empowered Temporal Gossamer needs to be changed. I’m of the opinion there is a bug here but I’m not convinced as to which element is the bug.
If you complete this quest in a group with an evoker on the legendary quest and use the item on the evoker, they gain the Empowered Temporal Gossamer buff as expected. However, leaving party with the person who gave the buff to the evoker removes the buff even though that player can no longer complete the quest again were the evoker to deputize them a subsequent time. It is my opinion that this is probably a bug.
The second odd behavior is that if you, as the evoker, deputize yourself after picking up one of the three eligible professions and then complete the Empowered Temporal Gossamer quest for yourself…the buff stays on you. Permanently. Like, even after you have already crafted the legendary. This also seems like a follow-on bug from the first behavior, wherein the buff is never removed because you can’t “leave party” with yourself.
To solve both of these scenarios, the buff should simply be fixed to only be removed once the evoker crafts the legendary regardless of who gave it to them. It’s a weird requirement to need to attempt to confine the legendary farm to a single play session by having the buff be removed if your crafting friend can’t stick around or has to go for any reason.