It might be instructive to run this from the command line with the debugger enabled. Step through the script and pay particular attention to what happens when you play with the values of "$newer_option". If I were held to a quick bet, I'd say that you are passing an invalid option or directory to your tar(1), and it's throwing up its hands. You can check this by looking at the returns from the C<system> call

my $ret_c = system ( ... );
print "$ret_c\n");
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If this were me, I'd also do some sanity checking on the parameters, just to make sure that they were what I expected them to be, not that anyone would try to insert malicious code starting with a semi-colon ....

Finally, your filter-loader doen't seem to be involved at all in this test script. Was that intentional? Or does the new-filter get installed between tar(1) and the input file-list?