This violates Rule A in https://twiki.cern.ch/twiki/bin/view/CMSPublic/FWMultithreadedDataProductsThatNeedToBeChanged "const functions must return the same value ginen the same arguments". Calling 'SetUserContent' changes what is returned from the 'GetUserContent*' family of functions.
This need to be reported and this interface must be removed from this class or this class can no longer be placed into the Event.