A job that inherits from multiple parents who are each trying to Provide configuration files will only ever get the configuration of the last parent added.  To reproduce:

1. Create 2 configuration files in Manage Jenkins -> Managed Files
2. Create an Inheritance Project the Provides configuration file 1.
3. Create another Inheritance Project that provides configuration file 2.
4. Create another Inheritance Project that extends the previously 2 created files.  
   One would expect that this job should receive both configuration files to consume, but it will only get the one from Project 2.