As Covenant elluded to, this 'fix' seems like an attempt to pacify the angry horde, rather than actually 'fix' anything. My tests show confirmed duped items having no issue being placed on vendors. My tests also have a fresh hat of the magi not being able to be placed, fresh as in 2-3 hours old. I have 2 character transfer tokens purchased from Origin.com , only a few weeks ago, neither can go on a vendor.
This is obviously not functioning as intended. The fact they decided to include it the way they did with a few days testing on test center has me more reminicent of the "axe the retreive container" than of [insert properly deployed system in the last 3 years.. i'll wait]
Really, test this, I don't use vendors so it's not really going to impact me but I'm sure a lot of people who don't bother with this corner of the internet are going to be thinking wtfmate.
I'm starting to really think we need a new dev team. I don't carry torches or pitchforks, and they've done a lot well, but this is a big thing to mess up. As are most things when they do mess them up, it always feels rushed, like they need to put content out to keep the suit and tie above them happy. Just give us a healthy game, and spend more time testing please.
Goodness.