Iron trapdoors pushed by pistons while being triggered keep their state until they get updated by powered blocks(and unpowered again) or unpowered redstone. Block updates do not change their state. This bug is caused by the fact that iron trapdoor's code it's pretty much a carbon copy of the wooden trapdoor's. This may work as intended , giving players a new type of wall cover. This bug it's harmless and doesn't break any features or affect the gameplay.
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Is this still a concern in the current Minecraft version? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases. If this has been done, we can reopen the issue.
Keep in mind that the "Resolved"-Status on this ticket just means "Answered", and that we are waiting for further information on whether this issue still exists or not. We will reopen it as soon as the requested information has been delivered.
Iron trapdoors used as a cover on a vehicle.