Mixins, config:{} and control inconistencies

Can someone explain how config merging works with respect to mixins and controller.config.control?

Please see these examples:

• control property:
  
  
  
  • Mixin has reference=foo
  
  
  • CtrlA has nothing
  
  
  • CtrlB has reference=baz
  
  
  • Final control is reference=baz as reference=foo is lost
  
  
  
  


• something1 property:
  
  
  
  • Mixin has reference=foo
  
  
  • CtrlA has reference=baz
  
  
  • CtrlB has reference=bar
  
  
  • Final something1 is reference=baz and reference=bar, foo is lost
  
  
  
  


• something2 property:
  
  
  
  • Mixin has reference=foo
  
  
  • CtrlA has nothing
  
  
  • CtrlB has reference=bar
  
  
  • Final something2 is reference=foo and reference=bar, foo is not lost
  
  
  
  

Why is something2 handled differently than control? Is this the desired behavior?

What are the rules for when a mixin's configs are merged vs replaced?

Mixins, config:{} and control inconistencies