Are they trying to rethrow the die? And then you catch it again. Try this: 
if ($SIG{__WARN__}) {
      my $previous = $SIG{__WARN__};
      my $caught = 0;
      $SIG{__WARN__} = sub {
          return if $caught;
          $caught = 1;
          # do my stuff
          my $ret = $previous->();
          $caught = 0;
          return $ret;
      };
    }
    else

[download]
If they catch the fact that you are in the call stack you might want to leave the goto in, but then you are limiting them to one warning in the entire script.

UPDATE
Oops. I forgot to call the ref. :-(

Worse than that, the solution is too complex and misses the cause of the problem. See the response I have down below. Just drop the goto and the original code works.

In reply to Re (tilly) 1: How can two modules latch onto $SIN{__WARN__} or $SIG{__DIE__}? by tilly
in thread How can two modules latch onto $SIN{__WARN__} or $SIG{__DIE__}? by rrwo

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