Sometimes it works, sometimes it doesn't which is very annoying. Basically, in the town I was trying to add a 3/5 defense rate mod to my new medallion. The end result was i lost crafting materials and medals as expected, but the mod DID NOT end up on my new gear as desired. In fact, the original item disappeared too so it was a complete lose-lose situation. Something that might be worth noting is that the item I tried to add this mod onto was upgraded from mythic to legendary. I have a hunch this might be the culprit, as that forces an extra mod slot onto the item and that was the slot where I tried to tinker. Just a hunch though.
Repro Chance: 50%
Steps for Bug Repro:
1) Go to town
2) Tinker as usual (literally just normal steps, nothing fancy)
3) You lose crafting items, defender medals, and the original item; the mod is NOT on the new item.
Disclaimer: Again, as mentioned above, I SUSPECT this has to do with the 3rd slot that was forced onto my item when upgrading from mythic to legend.Expected Results: 1) Go to town
2) Tinker as usual
3) Actually have the desired mod on my new item.