Affects Version/s: Minecraft 14w21b, Minecraft 1.8.2-pre6, Minecraft 1.12
Fix Version/s: None
Use /setblock x y z wooden_door 0 replace, where x y z is the location of the bottom half of an iron door.
The iron door should disappear, and be replaced with a wooden door.
The iron door disappears, as expected, but the wooden door is dropped as an item, instead of being placed.
Replacing the top portion of a complete door of either type with any block, including air, causes the door to drop as an item.
Replacing the bottom portion of a complete door with any block, including air, causes the door to disappear.