User blog comment:Scooter8pie/Transparency Bug/@comment-4583259-20121127091735

This is important enough that I've decided to add articles about it. See Transparency_cheat for the technique of deliberately going into solid rock (I described a simpler way to do it where you can just go 3 blocks straight down).

The "occurring naturally" version of the bug is described in the Renderblock article near the end.

Also see the One-way_doors article, which shows another way to get stick inside a block.