I and my mate went through dungeon countless times just to get the right weapon. Finally, it dropped! My mate had nothing in blacksmithing so I went to upgrade it for him (still almost 2 hours on trade timer). First I've tested with another item if upgrading it will make it bound. Success! No issue. Then I've tried to upgrade the very weapon we've farmed so long for. In the preview, the resulting weapon was shown as not bound. I've upgraded it, and suddenly it became bound and timer disappeared. I've learned it the hard way...just giving heads up for those who don't know. Looks to me like a bug.