I think it's fine to log in that situation, where they have a properties key that is deprecated (even if its value is mirrored in another key). 

I've changed the ConfigKeys deprecation warning stuff to log.info if there is a deprecated key in there whose value matches that of the non-deprecated key.

I guess one might be doing that for a backwards compatible brooklyn.properties that works against 0.5 and 0.6 though...