Jimmycon99

My 1999 XT600E has a starting problem. Sometimes (twice now) when I thumb the starter, the engine cranks over but does not start. When I lift off the starter button, it keeps cranking. Then I remove the ignition key and it still keeps cranking. By this time, I undo the leads from the battery, but it is too late - the starter relay has fused its contacts and burnt out. My mechanic and his auto electrician cannot explain what is causing it! The starter has been thoroughly checked out as have all the switches. Has anyone else had this problem?