I've only seen this on vendor in Brinlow Vale (so far). I click once to Buy/Sell and it goes fine. I close it out, click again, and the menu will not come up. I need to exit the street and come back.
Did more investigating... I can jump up and get the blue highlight on the vendor and then [enter] for the menu the second time, but the first time the vendor is just as high and the blue highlight comes up just when I pass by. I'm not sure what is different the second time that prevents the blue/menu coming up unless I jump.