Dispensers dispenses bucket instead of take up the waterblock/dispense the water from the bucket

I put one bucket of water and one empty bucket in a dispenser and put a waterblock infront of the dispenser.

What I expected to happen was...:
The bucket with water would dispense the water OR the empty bucket would pick up the waterblock.

What actually happened was...:
The dispenser threw out one of the buckets. (This only happens when there is no water infront of the dispenser)

Steps to Reproduce:
1.Put one bucket of water and one empty bucket inside a dispenser.
2.Put a water block infront of the dispenser.
3.Link the dispenser to a button.
4.Press the button sesveral times.