Trying to place down Iron or Wooden Trapdoors does not work when pointing on top of block in gamemode 1 or 0. trapdoors can be placed when pointing at the side of a block though. This might happen to other blocks as well
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MC-55241
iron or wooden trapdoor cannot be placed
Resolved
Invalid
0
Intended.
While not an authoratiative source, the MC Wiki states that trapdoors "can only be placed on the side of a solid block."