Yep, the problem is with the matching done inside of diagnostics.pm at the reported line. If before this line one adds

    utf8::encode($_) if utf8::is_utf8($_);
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on line 552 of the diagnostics.pm then the problem goes away. Well, actually this problem goes away, instead the Carp.pm fails, again with regex matching.

Global symbol "$c" requires explicit package name at test.pl line 8.
Execution of test.pl aborted due to compilation errors (#1)
    (F) You've said "use strict" or "use strict vars", which indicates
+ 
    that all variables must either be lexically scoped (using "my" or 
+"state"), 
    declared beforehand using "our", or explicitly qualified to say 
    which package the global variable is in (using "::").
    
BEGIN not safe after errors--compilation aborted at /usr/lib64/perl5/5
+.12.2/Carp.pm line 113.
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Really weird problem. Things work fine for substitute but fail for regular matching.

Looks like this bug happens to be only in $SIG{__DIE__} handler. At least I could reproduce it in

use strict;
use utf8;
BEGIN
{
    $SIG{__DIE__} = \&report;
    sub report
    {
        my $arg = shift;
        $arg = "'$arg'" unless $arg =~ /^-?[\d.]+\z/;
        warn("Done\n");
    }
}

$c;
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