c1 zocchi 2 shoe broken shoe

what would cauce the whole pad on one of the clutch shoes to come completely off .was riding a c1 with the zocchi clutch upgrade put the bike on the stand to pull the spark plug and look to see how the bike was running (only about 1.5 gallons of gas through the bike) went to start the bike and the pull start would not pull took off the clutch cover and the whole pad on one of the shoes was off

if the clutch pad heats BEYOND what it is built for, it will harden, crack and break in half.