While most noticeable with trap doors that have handles, all trap doors when facing north or south have their bottom texture oriented incorrectly. In the east/west position, the handle on the trap door is matched both on top and underneath of the trap door, while in the north/south direction, the handle is on the other side and does not reflect where it should actually be positioned on the item. Please see images for reference and the guide below on how to reproduce this.

To reproduce:

1. Create a new world in creative with any seed.
2. Find yourself an open field.
3. Get a locator map from the creative inventory.
4. Open the map.
5. Orient the arrow representing the player to point to the top of the map. Congrats! You have found the cardinal direction north!
6. Build a 6 wide by 5 high wall made of a light coloured block on the north/south axis (This wall will be referred to as Wall #1). Go ahead and do the same on the east/west axis (This will be referred to as Wall #2). Go ahead and label them with a sign for easy recognition.
7. Note that Wall #1 on the n/s axis becomes the wall on which trapdoors are placed facing the east or west. This while Wall #2 on the e/w becomes the wall on which trapdoors are placed facing north or south.
8. Place any trapdoor (preferably birch, acacia, or jungle, as they are handles and are easier to see) on the middle of the both walls.
9. Observe that on Wall #1 , the handles of the trapdoors match both on the top and bottom, while on Wall #2, the handles do not match, the top is in the correct position away from the wall while the bottom is incorrect as it it against the wall.

Observed result:

Trapdoors facing North and South have incorrectly oriented bottom textures.

Expected result:

Trapdoor texture is the same on the bottom as it is on top as to have door handles that match on both the top and bottom the way they do match when placed facing east and west.