Using Block 63 or 68 (Signs) in a superflat preset causes minecraft to crash

Using Block 63 or 68 (Signs) in a superflat presets causes minecraft to crash.
Crash is attached
Note that the crashes are different for the version used.
Steps to reproduce:
1)Go to "create new world"
2)Go to "More World Options..."
3)Choose "Superflat" world type, and go to "Customize"
4)Go to "Presets"
5)Replace the text at top with "63" or "68"
6)Click "Use Preset"
7)Minecraft crashes