I purchased a brand new Omega Seamaster co axial chronometer today. When I arrived home I unscrewed the crown to set the date and time, when I pulled it out after unscrewing the few turns the entire crown with stem pulled put of the watch, is this normal, I pushed it back in and set the time and date and screwed back in against case and everything seems fine, is it normal , shouldn't the stem have something inside the case that prevents it from coming out further than the third notch ?

 

Take it straight back to the person you bought it from.
If it is indeed brand new then warranty will cover it.