Villagers spread unprompted negative gossip - Trades anger villagers

I have been trading with the villagers in a nearby village across multiple worlds and no matter what I do, the trade prices always seem to increase rather than decrease. I have not attacked any of the villagers and the worst I have ever done is wake one up, and/or loot a chest but trades keep costing more. Are the villagers supposed to increase trades after actions like that, or is it simply a bug?

 

Edit: I have done some testing in a creative test world where the villagers were isolated and have found that the act of trading with them causes the villagers to like us less, not more.