I had thrown wheat seeds near water by accident when it first happened. After making sure it wasn't a one-time fluke, I realized it was a bug.
Steps to reproduce:
- find a source of water
- throw an item near the water so you can see the water from directly behind the item
- you can throw the item onto a glass block or barrier to see it better
- beds and most blocks will not produce the bug
- thrown glass blocks (including stained glass), barriers, and doors will produce the bug
- placed glass (including stained glass), barriers, and doors will not produce the bug