Villager keep changing proffesion even if it's already have one at max level

It's happened Twice to me, i have 2 Villager with both have their own job at max level (armorer and farmer) and somehow, they two changing job into fisherman in front of me! I see the green particle too, those Villager keep the max lvl trading though, but i hate it when it's happened, because my base is surrounded with barrel. Please fix this