The bug

Shulkers will teleport to glass and leaves now (19w13b) - I also tested it in (19w13a) were they didn't do it.

Steps to Reproduce:

1. Create a flat world using "The Void" preset
2. Stand on the cobblestone in the center
3. Run the command:
   (easily creates a single block in a void world)

   /fill ~16 ~-1 ~16 ~-16 ~-1 ~-16 air replace stone
    

4. Spawn a shulker on the cobblestone
5. Place a glass or leaf block near the cobblestone
6. Break the cobblestone

Expected Result:

The shulker would not teleport to the glass or leaf block.

Observed Behavior:

The shulker teleports to the glass and/or leaf block.

Notes:

Related to MC-83695, and could be Working as Intended based off of its resolution.