If you download the texture packs: Natural and Plastic Texture pack from the marketplace and you apply one of them, you'll see that some textures of these texture packs look off.

The Natural Texture pack and Plastic Texture Pack have some textures that randomly rotate as the vanilla textures do, but some of the Plastic/Natural textures aren't made for this, so it looks kinda odd. There are some textures, like stone, that are already adjusted, some textures like Netherrack aren't.

If you look at the Netherrack and Stone comparason for the Natural texture pack for instance, you can see that they both use the same texture, just coloured differently. This is mostly fine, except that the Netherrack texture randomly rotates while the Stone texture does not and this is pretty inconsistent.

The Stone texture is adusted to not rotate, unlike the vanilla textures, because otherwise the stone textures don't connect with eachother, which would look odd. Sadly the Netherrack isn't adjusted and some other textures from both the Natural and Plastic texture pack have the same problem, which makes tese textures not connect with eachother, which looks odd.

From what I have found, the problematic sprites are:

-Netherrack

-Magma Block

-Sand

-Red Sand

-Glowstone

-Obsidian (Plastic only)

-Dirt (Natural Only)

-Terracotta (Natural Only)

What should happen is that these textures get adjusted to not rotate randomly, like Stone does in both the Plastic and Natural Texture Pack, so that they connect with eachother and overal looks a lot better.