The problem is caused by a computer screen (the initial log-in terminal) still active behind the barter menu. Both the computer screen and menu are fighting for control of the cursor. The barter menu works perfectly if you make sure your cursor when using the barter menu is outside the screen space of the computer behind it. This means the empty space just to the left of the item names on the left, and the prices on the items on the right. If you stay in these two areas with your cursor, browsing, selecting, and buying work perfectly.
An annoying oversight by the developers, but one easily worked around once you know the trick.
Not sure that I know what the barter menu is. So far everything related to barter that I've seen is either after turning an even level, I can upgrade the skill. Or in dialog option i.e. Barter 25/50. You're saying there's a whole barter screen that is supposed to pop up when interacting with the terminal? I'm only seeing the terminals inventory on the right hand side and my own on the left.
Any word on successful purchases from the terminal making its way into the room? I don't remember all the options right now, but I thought there were a few physical ones that I would expect to see actually sitting in the room somewhere after I buy. (Fridge is the only one I can recall right now, but I thought there were a few more).