The pilot was conducting practice forced landings in the training area. When overshooting from one of these approaches he observed that the flap would not retract from the two stages down position. After advising the flying club by radio of the problem, the pilot returned for a landing. The aircraft bounced on touchdown and then began to porpoise. The nosewheel was dislodged and the aircraft slewed off the runway before nosing over onto its back. The flaps had failed to retract because of a faulty micro-switch. The pilot had not experienced a malfunction of this nature before and had allowed this to distract him from the operation of the aircraft. He had persevered with the landing after the initial bounce, but had not been able to exercise adequate pitch control.