Factorio Forums

When walking directly next to a cargo wagon, your player model hides beneath the cargo wagon for the top half, and walks over it for the bottom half, If you walk straight past it, it looks like you're teleporting up and down (https://gyazo.com/f18ccc81455be7689b7365cb8bb9182b)

Since the game is 2D it does not get depth information natively so it is depending on a few broad rules for figuring out what is on top, what you see is a result of shortcomings of that method.