On AIX I've seen problems with giving garbage mode bits (e.g 0) to the equivalent of a sysopen call cause problems later accessing the file, even for the owner. I thought that there was a slight chance that perhaps a bad umask could cause the same problem (though very unlikely). But even why I try that I can't reproduce it (i.e. this works fine for me on perl 5.8.5...)

% umask 777
% perl -le 'open my $fh, ">foo" or die "open:$!"; print $fh "hello" or
+ die "print:$!"; close $fh or die "close:$!"'
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