Been having this problem for AGES! finally caught a pally bot standing in front of a vendor trying to equip a green item (he should have sold) however he was stuck at the "equipping this will bind it to you". Lucky for me this was a green item and the prompt came up, for a grey / white looks like bot would have equipped...
I attached the log- looks like the bot was there for a bit ~50 mins.
I think the important thing here is the vendor Kaeyendis Shimmersteel - was a Horde only vendor in Talador. As an Ally i could not get a trade window up to the NPC so it looks like the bot got creative and tried to equip?
While i use the profile all the time- it does not have vendors defined... so hopefully if i define some Ally vendors around the place.. and black zone around that vendor i may have chance.
TL;DR - looks like it happens when you try talking to a bad/difficult vendor..
8 Dec 2015 15H09.log.html