I had set my world border to 100, then I told it to close back to 15 blocks in 20 seconds (/worldborder set 15 20) and I decided to race it in survival. I died because the wall caught up, and when I tried to respawn, it stopped responding.
Environment
Windows 7 Home Premium - V6.1 (Build 7601: Service Pack 1)
Java 1.7.0_51
Probably caused by this: MC-54228
but this is now fixed