Does anybody know the reason for the issue in the first part of the tutorial (http://rpiplayground.wordpress.com/2014/05/03/hacking-the-gpu-for-fun-and-profit-p

Does anybody know the reason for the issue in the first part of the tutorial (http://rpiplayground.wordpress.com/2014/05/03/hacking-the-gpu-for-fun-and-profit-pt-1/ http://rpiplayground.wordpress.com/2014/05/03/hacking-the-gp...)? "NOTE: Occasionally, the GPU can get into weird states where the programs do not return the expected values. I have not determined if it is a bug in the host-side code for managing the GPU or if there is something else going on. In any case, if you see things you don’t expect, try rebooting the machine."