When trading with villagers, they will sometimes exit the interface on their own. When this happens, I'm often mid-click, causing me to unintentionally attack the villager. Other times, I'm moving items, which will then be dropped and potentially "stolen" by the villager. This issue often occurs with farmers, suggesting it may be intentional, put in as a troll. If so, there should be some sort of delay for attacking to prevent the player from accidentally hitting the villager.

I was hesitant to report this issue, as it is difficult to recreate reliably, but hopefully others are having the same issue and can verify its validity.