Item frames (no matter if empty, with an item or a map) are not rendering when obscured by an semi-transparent layer of your skin.

My skin has goggles which glass of are on 25% of transparency. While the skin is in front of a greenscreen, made by the use of fully green maps placed in an item frame on top of a light source (in my case sea lanterns), when looking at the skin, you can see the item frames not loading and instead of green background, the texture of sea lanterns is visible.