I started with 'use Apache::Bootstrap 0.06;', but that caused an UNKNOWN cpan testers failure, with the error "Can't locate Apache::Bootstrap...". So I checked the error number passed back to the shell for that failure and it was 1.
I checked the error number passed to the shell for 'use 5.8.6;' pragma in a Makefile.PL that didn't have that version of perl, and the error number was 255. My theory is that Test::Harness or something is picking up that error code differently, since these occurrences are represented in CPAN tester reports as NA.