The bug

You can't pick anything up if you stand in the water pipeline near a half block if you don't move (Your coordinates don't change). You can pick items up if you move, and you can't pick items up if you don't move.

How to reproduce

1. Create a water pipeline, it should contain any type of the half block at the end of the water flow. See the attachment.
2. Stand in the water pipeline, near the half block.
3. Use a dropper to put items in the pipeline.
4. If you move, you can pick items up. Otherwise you can't.

Plus: If any blocks placed at the top of the half block, you still can pick items up without moving yourself.