can anybody please shed some light on what's happening?

everytime i press my clutch pedal down abit harder than usual the piston comes out of the clutch slave cylinder leaving me with no clutch!

it's happened twice to me/ After the first time, i re bled the clutch and set everything up again as it should be. It was fine when i drove for a couple of days but then i let my friend drive the car who has a heavy foot (both) and he must have banged down the clutch pedal during gear change... and pop! the clutch pedal never came back up. after inspection i found the piston in the clutch slave cylinder had come out too much and the clutch fork was stuck all the way forward and not coming back!

i've never had this problem before and it has baffled me. if you have any suggestions please let me know asap.

cheers