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  1. Minecraft: Java Edition
  2. MC-157645

Mobs cannot pathfind properly on bottom slabs, farmland, dirt paths, and other blocks without a solid top face

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    • Icon: Bug Bug
    • Resolution: Unresolved
    • None
    • 1.14.4, 19w38b, 1.15.1, 1.15.2, 20w11a, 20w12a, 1.16 Pre-release 4, 1.16 Pre-release 8, 1.16 Release Candidate 1, 1.16, 1.16.1, 20w28a, 20w30a, 1.16.2 Pre-release 1, 1.16.2 Release Candidate 1, 1.16.2 Release Candidate 2, 1.16.2, 1.16.3 Release Candidate 1, 1.16.3, 1.16.4 Pre-release 1, 1.16.4 Pre-release 2, 1.16.4 Release Candidate 1, 1.16.4, 20w45a, 20w46a, 20w48a, 20w51a, 21w03a, 1.16.5, 21w05a, 21w05b, 21w06a, 21w07a, 21w11a, 1.17 Pre-release 2, 1.17, 1.17.1 Pre-release 1, 1.17.1, 1.18.1, 22w16b, 1.19.4
    • Confirmed
    • Mob behaviour
    • Normal
    • Platform

      The bug

      Mobs cannot pathfind properly and thus move very quickly on blocks without a solid top face, especially if there is air or another block without a solid top face below.

      This is known to affect the following blocks (list may be incomplete):

      • Bottom slabs
      • Farmland
      • Dirt paths
      • (Empty) end portal frames
      • Enchanting tables
      • Carpets above string
      • Chests
      • Campfires

      It seems to be affecting all mobs, though it seems like the issue is best reproduced with skeletons due to their strafing.

      How to reproduce

      1. Create a "Redstone Ready" flatland world
      2. Run (optional, but makes the issue easier to see) 
        /fill ~ ~-2 ~ ~20 ~-12 ~20 air
      3. Run 
        /fill ~ ~-1 ~ ~20 ~-1 ~20 oak_slab

        (Or any other affected block)

      4. Give yourself some skeleton spawn eggs
      5. Switch into survival mode
      6. Spawn a skeleton on top of the slabs
        → The skeleton moves really quickly

      Example

      Here is an example in video: https://youtu.be/rNsKKNCFxMM

            Unassigned Unassigned
            Biggles Casimir Leja
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            27 Vote for this issue
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              Created:
              Updated:
              CHK: