I note you're running blead (5.11.0). The problem there might lie with something other than Math::Pari (eg Test::Harness).
I get the same error with a fresh compiled 5.10 and Test::Harness 3.10.
From where does one obtain the perl-5.11.0 source ?
Have a look at http://dev.perl.org/perl5/source.html.