Dispensers with an empty bucket destroy waterlogged stair blocks

I was experimenting with the new water physics, and I wanted to see how dispensers with water buckets affected stairs. At first, I thought it was behaving normally. I placed a water bucket into the dispenser and a stair block in front. Upon pressing the button, the stairs became waterlogged. This is good, expected behavior. When I hit the button again to remove the water, it removed the entire stair block, with no item drop.
See this video.