Dropped items in flowing water next to fences teleport back repeatedly

Dropped items appear to get caught in the gap between fenceposts and flowing water next to them, and may teleport back and forth between two points.

Steps to reproduce:

1. Create the device in "Flowing 1". There is one water source block in the lower-right corner, where the cursor is pointing.
2. Throw an item into the water flow, so that it moves straight into the fence. (Flowing 2)
3. Place a block in front of the water source block, forcing the water to flow around it. (Flowing 3)

• The item will float downstream, approximately to the point in "Flowing 4", and then teleport back to the fencepost.