Proper way to create logins on Always on
Logins and users work the same way they do with DBM or log shipping. If using SQL Server authentication, you have to sync the SIDs manually (or manually create the login with the right SID) assuming the login is already created on the other instance. 

Either way, this is not automatically done. You need to create the login at the instance level to match the DB user. If using Windows authentication, it should have the same SID, but you still need to create the login at the instance level. 

Remember, the instance-level login sits outside the AG, so the AG won't do anything there. Not sure why you thought the AG would work this way; it never has, just like DBM and log shipping.

Also, there is no feature called Always On. Please do not refer to AGs that way. http://sqlha.com/2013/04/29/alwayson-is-the-new-activepassive-and-activeactive/