Actually, the team have just put in a fix for this in 4.2. As it is a client issue it can’t be fixed before then. I’ve added it to Known Issues so you can keep up to date there.
When 4.2 releases anyone currently affected by the issue (without the Trophy) or anyone who plans to unlock it will need to Upgrade their Treasure Hoard. This will trigger the renown to recalculate and the Trophy to be registered.