That's not a bug. It was said that they intentionally made the C5 weapons available only to specific weapon trades.
Yup its the same thing with a Great Pata or any other Top C Weap, you cant driectly change it to an Elctpic Sword/Axe, you have to change it to and another Weap 1st like a Ghoul Staff.
Just keep switching it till you can get the weap you want, its that simple.
That's not a bug. It was said that they intentionally made the C5 weapons available only to specific weapon trades.
but ... why? o.O
It just makes no sense... it's not as if there's any big quest or huge crafting attempt behind switch from weapon A to B so that you can get weapon C. And it sure as hell does not increase "fun". It is just another mouse click. But why introduce that?
I cannot see any logical reason for that, except if they intentionally want to piss off players because they now have to click around to find the trading combination which works.