The orientation for the dark oak trapdoor and the iron trapdoor textures that were added into Minecraft 1.13 has its textures orientated from a north to south position. The other trapdors: oak, spruce, birch, acacia, and jungle, all have their orientation go from south to north. It is hard to notice the difference, but if you pull up the texture of the doors in the minecraft.jar and then look at the textures in-game you will find their orientation reversed. I was only able to notice it when I started creating a resource pack and found my handles being reversed on only the iron and dark oak trapdoors.
It is a very minor inconvenience due to having to flip the textures when creating a resource pack, but it is a bug nonetheless due to it only affecting these two trapdoors.