Allowing a stored procedure to select from a system table using a certificate in SQL Server 2012
Although I do not understand why it would react different in 2012, I do wonder if you could work around it by using the EXECUTE AS <certificate_logon> clause in the CREATE PROCEDURE.
In theory this should be equivalent as to your solution as the default isEXECUTE AS owner, but maybe it reacts slightly different ??? Worth a try I think.