I've a similar problem on RH8. I'm trying to port a a running application, and the xml parser is returning the same panic error when my handler returns. I tried unsuccessfully to use the variable substitution you mentioned, so I was wondering if you're any futher along. 
s{ <\?nm(             # opening angle bracket
    (?:   # Non-backreffing grouping paren
    [^>'"] *  # 0 or more things that are neither > nor ' nor "
    |     # or else
    ".*?" |     # a section between double quotes (stingy match)
    |     # or else
    '.*?' |     # a section between single quotes (stingy match)
    ) +              # repetire ad libitum
    #  hm.... are null tags <> legal? XXX 
    )\?>          # closing angle bracket
}{my $var = $1; my_handler($r, $var)}geisx;  # mutate

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In reply to Re: Re: Functions in substitutions (s///) and Perl 5.8. by jmarans
in thread Functions in substitutions (s///) and Perl 5.8. by v_thunder

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