Empty buckets in dispenser not properly picking up water

I filled a dispenser facing an infinite water source, with stacks of empty buckets. I expected that when powered, the dispenser would attempt to fill one of the buckets in its inventory with water, but having no place to put the new item, it would drop the filled water bucket out of the front... but instead, when powered, I hear the dispenser click, and see that water has been picked up, but there is no water bucket to be found. One bucket is missing from the dispenser, also nowhere to be found! Plays twilight zone music (On a serious note, there goes one perfectly good water bucket 😞 )