Test::More wait status non-zero but all tests pass

karpet has asked for the wisdom of the Perl Monks concerning the following question:

I maintain several CPAN modules. Lately I've been seeing cpantesters output like this for some XS/C modules:

t/00-sanity.t       (Wstat: 139 Tests: 3 Failed: 0)
  Non-zero wait status: 139
[download]

It seems to be FreeBSD in particular that has the problem, with all current versions of Perl.

It's clear from the output that the tests are all passing, but because of the Wstat being non-zero, the overall report is a Fail.

Suggestions on how to debug this? My googling turns up a couple of other reports of this but no answers.