I want to get the Master Crafter, reported as bugged from Steam players! I fully maxed my Elder Rapier of Extraordinary Luck, even kept upgrading it after bars were displayed as full, with +1 weapon damage. It is fully maxed but no achievement. Some other players suggest maxing a Legendary only and that this worked for them... What to do? How can i get that nasty achievement? Soon, i am going to complete them all, so i really, really need this specific one!

I think you need to have weapon which would show
"Weapon level 50" http://i.imgur.com/RST5m1F.jpg
when maxed, You posted that you maxed one at level 44, it isn't perfect:)

Sometimes, while using transmutation, game becomes temporarily bugged. Doesn't display the changes that will occur when you transmute, like the +1 to damage, even though you do the enhancement. Or erroneously reporting the item is fully upgraded; but if you exit to main menu and play again, now it gets enhanced properly until maxed. Phew, finally got it!