Custom Villagers "Disagree" When You Attempt to Trade

Earlier this morning (when it was still 1.14.2), the admin of the server implemented a villager to sell the heads of players for one emerald each. Players (including myself) were able to purchase heads as we pleased. Once the server updated to 1.14.3 (which it does automatically), the villager shook his head and disagreed (see: subtitles in bottom right).