I am lvl 60 and have beaten hell difficulty. I have not done any quests on inferno yet. When I enter a hell act 4 game and then leave; I am able to join a public inferno act 4 game. I can not create an inferno act 4 game. This is the same with every quest I have tested so far.

Enter a hell game. Leave. I can join the same quest on inferno using public games. I have not done any inferno quests.