This is probably not a problem, but you are not creating hashrefs that contain other hashrefs. You are creating hashrefs that contain a copy of the contents of other hashrefs. They are not bound to eachother in any way, later changes in one do not affect the other (but you said they are constant anyway).

  
 ( %{ make_hashref() } )
  # makes a (shallow) COPY of the data in the hashref
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