If the player has translucent/semi-transparent pixels on the second layer of a character skin, they will make the layer behind it invisible, but only at certain angles.

You can see this in the images attached, affected by the glasses on my skin that use translucent white pixels.

Two of the images have the bug shown, but in one of the images the bug doesn't appear (this is to demonstrate that the bug only appears when the player's avatar is facing certain angles.) My skin's texture is also attached.