Without pics of the piston it's hard to say what his problem was.
Too lean?
Depending on the piston being ran Cr500's need to be relieved at the exhaust bridge, or oil holes drilled in the piston, was it?
Improper piston to cylinder clearance.
Incorrect oil ratio in the fuel or bad oil.
To hot of plug range, ect....
But running it up on a dyno I would not think it would need the throttle blipped because there is very little deceleration resistance, so slowing it down takes just a few seconds and I would not think that would cause a problem. Hopefully some of the guru's here will chime in...
Unless you are running it wide open in top gear for a while and then letting off the throttle and coasting in top gear you should not have any problems.
But, if it makes you feel better, blip the throttle, I do because it sounds cool