Here’s a fix that appears to work:
From JustJoe’s original post:
Try this:
1. Unequip the item you want to reroll your MW on. Put it in your chr local inventory.
2. Unmark it as junk or a favorite. No marks. Just vanilla item.
3. Quit game. Don’t just log out, Quit completely, to desktop.
4. Log back in.
DO NOT RE-EQUIP THE ITEM!
5. With item unmarked and sitting in inventory, Reset MW on this item at Blacksmith.
6. Quit game back to desktop again.
7. Log back in.
DO NOT RE-EQUIP THE ITEM!
8. MW item to level 4, with it unequipped and unmarked in inventory.
It should choose a truly random affix this time.
Maybe having it equipped and/or marked as a favorite that causes the glitch.?
Seems so. Try this and see if it works for you.