I don't have any practicle experience with Parse::RecDescent, but i remember seeing this the other day when skimming the docs for another node... 
# Global flags (useful as command line arguments under -s):

      $::RD_ERRORS       # unless undefined, report fatal errors
      $::RD_WARN         # unless undefined, also report non-fatal problems
      $::RD_HINT         # if defined, also suggestion remedies
      $::RD_TRACE        # if defined, also trace parsers' behaviour
      $::RD_AUTOSTUB     # if defined, generates "stubs" for undefined rules
      $::RD_AUTOACTION   # if defined, appends specified action to productions
did you try setting $::RD_HINT ?

In reply to Re: Parse::RecDescent gotcha? - duplicates in ORs by hossman
in thread Parse::RecDescent gotcha? - duplicates in ORs by qslack

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