Just a note; this affects the ladder code too. This feature is also supposed to work with iron trapdoors, so syrmorite trapdoor needs this when open.

Versions

Betweenlands version:

3.2.1-alpha-snapshot

Forge version:

Forge 1.12.2-14.23.1.2606

Singleplayer or Multiplayer:

Singleplayer.

Installed mods:

Appleskin 1.12.21.0.9
B.A.S.E 1.12.2-3.5.1
Better Fps 1.4.8
Better Placement 1.0.0-1
Client Tweaks 3.1.2
Clumps 3.0.0
FoamFix 1.12.2-0.9.0-Anarchy
Friendly Fire 1.5.8
Waila/Hwyla 1.8.23
Keyboard Wizard 1.12.2-1.5.3-b1
Mouse Tweaks 2.8
Ninja's Mods 1.12
Optifine 1.12.2 C8
perspectivemodredux-1.12.2-0.0.1
StepUp 4.0-mc1.12
SwingThroughGrass 1.12.2-1.2.3
TapeMouse 1.1.3.17
Texture Fix 4.0
The Betweenlands 3.2.1-alpha-snapshot
XYZing 1.0

Description of the problem

How to reproduce:

1. Place a trapdoor in the middle of ladders.
2. Try to climb it. It won't work.

Expected result:

As of 1.9 trapdoors can be climbed like ladders.
The official Minecraft Wiki states (under Trapdoor): "An open trapdoor may be climbed like a ladder if it is directly above a ladder and on the same side of the block."
https://minecraft.gamepedia.com/Trapdoor

Actual result:

It didn't let me climb it.

Pictures: