Works for me on Linux. What happens if you use tie instead of dbmopen? Or a different DBM module?

my $count = 10000;
my %PL;
use DB_File;

tie(%PL, 'DB_File', 'pl.dbm', 0777) or die "Can't create DBM: $!";

%PL = map { $_, $_ } ( 0 .. $count );

print scalar(keys %PL), '/', $count, "\n";
[download]