When water is behind glass, and above a block that is not full but also will not be destroyed* (a pressure plate in this case), when looking through the water the underwater surface texture (the “refracted light”) is rendered on blocks which should not have that texture rendered.
*I didn’t check to see if it happens when on a normal block.
Note: Glass structure is not a box. It has corners cut off in a way so it takes up minimum space.
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