The main reason for the clutch shoes melting to the inside of the clutch bell is the engine's idle speed was too high. If you have to use your foot or a curb to stop the car when it's supposed to idle, your idle speed is too high and the clutch shoes will melt eventually. When you have the brakes applied, the clutch shoes are still expanding and contacting the inside of the clutch bell. This contact (friction) creates heat, and although the clutch shoes are made from a heat-resistant plastic, the clutch shoes eventually melt into one solid mass and prevent the springs from bringing the clutch shoes into their normal position.

To solve this, you must remove the engine from the car chassis, take the clutch bell off the engine, and remove all the melted plastic from the inside of the clutch bell. Replace the clutch shoes and springs with their stock replacement parts then correctly adjust the idle stop screw. See your kit manual or the engine tuning sheet for the correct installation of the stock clutch shoes. 

At idle, the car (with receiver and transmitter turned on) should have its engine running at low rpm with no movement of the car.