I was messing around with the /setblock command, trying to spawn in double high flowers and with the help of mcedit giving me the data modifier for the top, was able to. However, when I went lower and lower, finally doing /setblock <coords> 175 7 for the top (I thought it had to change, but it seems 11 works for all tops), my game crashed giving an array out of bounds error. /setblock <coords> 175 1 seems to work, it is only when the modifier is 7 that it crashes.
It also seems that I got very unlucky with the world I was playing on. It must have saved right when I clicked the button for that command because now whenever I try to load it, Minecraft crashes. I tried the same on a new world and it crashes, but doesn't crash on load like the other.
1. load up/generate a new world
2. give yourself a command block or two (optional)
3. put the command /setblock ~0 ~0 ~1 175 7 in a command block/run the command yourself
4. watch the crash
Attached is the crash report I received.