It cranked and cranked and cranked!

Strange thing happen yesterday as I set of for the Beford meet.

Ignition on, dials do the sweep thing, hit the crank/start button, the engine cranked over, failed to fire, so off came my thumb and it kept cranking on its own! It wouldn't stop untill I turned off the ignition.

Everything started as you'd expect on the second go, and later when I set off for home.

Should I be worried?

Has anyone else had the same problem?