The bug

If you place an item frame down, and put a block in that item frame, then place a lever on the same block as the item frame, the block in the item frame will show z-fighting with the lever.

The issue seems to be with Minecraft's placement of the block in the world which is in the item frame. Although you can't see it in this picture, the top item frame has a block in it, and the top of the block is z fighting the top of the lever, this happens when the lever is both on and off. The item frame on the left of the block, as can be seen, has a block of glowstone in the centre, whose texture is in front of the lever's texture. This is the other way round in the item frame on the right: there is a completely hidden stone block, behind the front of the lever.