Selling the armor I was wearing (NCR Bandolier armor or something like that) caused a popup notifying me that I was no longer dressed as the NCR faction, I could not dismiss the popup and the barter dialog was only accepting some input. I was able to button mash to get input on to the barter dialog but when I tried to cancel the transaction the 'are you sure you wan't to cancel the transaction' popup had a similar problem. Button mashing got me back out to the game world where the 'are you sure' dialog remained on the screen and couldn't be dismissed (I was able to get rid of it by going in to the pause menu and then returning to the game).