"Ghost" Signs - Rendering Glitch/Bug

Doing a specific procedure to signs will make them ghost blocks, which will disappear after you reload the map. Since it's hard to explain the bug, I made a little map which tells you exactly how to reproduce it.

Just follow the instructions.

http://www.mediafire.com/download/wvsb3to40e25rgd/Ghost+Sign+Blocks+Rendering+Bug.zip