Spawner can block the top water / lava texture. Transparent blocks such as spawners (eg leaves, glass) have an exception and do not block the upper water texture like all other opaque blocks.
Steps to reproduce:
- Create a small body of water (3v3 water / lava blocks).
- With the next layer (1 height higher) place the spawner (the spawner can only be placed in the center, and any full opaque blocks can be used on the sides).
The spawner is blocking the upper water / lava texture.
The spawners do not block the top texture of the water (like glass and leaves), since the spawners are transparent.