All blocks which use the texture to indicate directional lighting (e.g. polished stone blocks) have a standard lighting direction - the top and left sides receive light, and the right and bottom are dark. While this device is also utilized on door textures, this does not always translate with the models - they can end up having the shading order horizontally flipped, which looks a bit weird and some details intended to look concave can appear convex and vice versa.

A simple fix would be to have doors use separate textures for left-facing and right facing, rather than mirroring an existing texture.