The "regains it concentration and continues casting" message is when they get pushed a bit (normal melee would push, as would bash/kick), but they passed the channeling check to avoid spell interruption. AFAIK stuns always interrupted your spells (at least from a player perspective), unless they were immune to stuns (eg giants). 
		
	
		
		
		
		
		
		
		
		
		
	
		
		
	
	
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