I ran into this as I was streaming and I made sure to place a note up on the Youtube to those that watch to not do as I do, but this is a bit of a bug and maybe even a bit of an exploit. What took place is that the Dragon Trainer wants a Bronze Dexterity Scale, I had one already equipped, so I decided to hand that in.

Well, because of the crystal in the socket, instead of taking it off your hands (which I later showed in the video how this is suppose to go with the Focus one), he doesn't and it stays in your inventory. Later he will still give you the chest scale, but you get an error write up on the text chat (which is also visible in the video).

You can see the bug here:
https://youtu.be/FZ0IzcKi8wg?t=39m43s

Hopefully this explanation and footage will help fix the bug so that others will not make my mistake. >__<
I feel kinda horrible about it really...