There's a new rule this year that was instituted as a result of the Joe Exter-Patrick Eaves collision in the BC-Merrimack game last season. As soon as any player loses his helmet for any reason, the officials are required to stop play.
Personally, I think the rule is an overreaction by the NCAA. Had it been in place last season, it would have done nothing to prevent Exter from getting his head smashed into the ice.