Microwave trips breaker

New to the forum. 11/06/13 replaced the capacitor, microwave worked fine. 12/03/13 replaced 25 amp fuse & reset breaker, microwave worked fine. 2/17/14 replaced 25 amp fuse (never tested the old fuse, just replaced it) & tested by boiling water (microwave connected to extension cord outside). Worked fine. Refitted microwave into cabinet, reset the clock & breaker, put water in microwave, closed door, turned it on & it died. Reset breaker, reset clock & tried again, same thing, died on me. Tried two more times, no luck. Reset breaker & clock & never tried to use it again. 2/18/14, put water in & it boiled, put food in & it heated up, seems to be working fine, fingers crossed. Does anyone have an idea what the problem was/is?
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