The most recent update (v0.199.169) broke some of the textures for 1/4 glass slabs. It can be either regular glass or the crystal armor or glass door block, but either way when they are placed adjacent to other 1/4 slabs that are not glass or crystal armor, they allow you to see right through the other blocks.
an example pictured right here of me looking through glass 1/4 slabs adjacent to some hull/armor blocks that are also 1/4 slabs. As you can see, I (and now you) are able to see right through them to whatever is on the other side.
an example pictured right here of me looking through glass 1/4 slabs adjacent to some hull/armor blocks that are also 1/4 slabs. As you can see, I (and now you) are able to see right through them to whatever is on the other side.