The UV mapping isn't done correctly on the Oak and Dark Oak trapdoors. Because the Vanilla Minecraft texture is symmetrical, it's not noticeable. It does become noticeable when applying a texturepack (screenshots with texturepack included).

All 4 trapdoors are hinged on the side of the Sandstone block, yet only the Jungle and Acacia trapdoors behave like they are. Oak and Dark Oak have their textures in North-South direction (always) when placed, and opened the texture just shows as it is, even when the trapdoor is upside down.