I was experimenting with the textures and noticed some odd behavior. Specifically, the 'platform_picture' texture from the inserters is being drawn behind the 'structure' texture of the loader. While it's very subtle with the default skin, you can notice it with the left or right orientation that grab items from another structure.

offtopic: It would be cool to have the option to use the textures from AAI-Loaders.

the problem is that the "inserter" is the main entity but the loader has the right picture (moving belt etc). So the loader should be on top (if possible it should even be the only picture drawn). But the inserter image is needed for blueprinting. So the ordering is that the loader sits "on top" of the inserter, but the inserter still has an image. I think that is the effect that you see.

I hear you about the AAI loader images but I already regret that I started supporting other mods as this makes the support effort increase exponentially. I am open to patches and PRs but I won't spend energy trying to figure out how to use those images myself.