Robots not under driver control- does it happen- do you determine why?

[quinxorin]

Our team has had some problems.
Our 2009 robot was always a little sluggish - we know it to be a bug in the programming.
Our 2010 robot usually worked well. There was one match where our robot began behaving eratically without control of the drivers. The entire alliance did, so we believe it was a field fault.
Our 2011 robot has not had any problems yet.

We usually place our radio somewhere exterior on the robot, but protected by a sheet of Polycarbonate. Our 2011 robot has it completely unshielded (it is in a position where it would be very difficult to be hit) but our 2010 robot had a piece of 3/8in Polycarbonate armor (yes, that's bulletproof).