OK, I think I understand fully now. Let me see if I can make sense of it here.
It did happen again. It was when I reloaded a saved game, entered a town, went to the merchant and asked about what caravans buy and sell. I had to CtrlAltDel to close the app; restarted, reloaded again... this time I Tabbed out and exited the town (prompting an IN GAME SAVE), re-entered the town, and spoke again with the merchant with no problems.
What I was mis-understanding was that when you exit a town (or battle) the game does a quick save; I thought you had to do a save-and-exit and re-enter the game but that would only cause the problem to happen again, no fix it.