A bug report has been filed on the WPILib tracker here:
http://firstforge.wpi.edu/sf/go/artf1719
The TL;DR is basically this: if you are connected via SmartDashboard, and you disconnect the connected computer's wireless while the robot is writing a value to the SmartDashboard, the robot may hang until the write times out.. which can be a few minutes.
I'm working on identifying a good fix, but I fear the best way to fix it is to use non-blocking I/O... which would be a rather large rewrite.