If anyone has any documentation to the contrary, please show me. Also a failure script would be of interest. I am currently relying on this behaviour in production and if it is unreliable, I would really like to know. In the meantime you can take the low-tech approach and run the following script from multiple xterms while trying to create a problem...

use Fcntl qw(:flock);
my $file = "my.lock";
open(FOO, ">> $file") or die "Cannot write to $file: $!";
print "Getting the lock\n";
flock (FOO, LOCK_EX) or die "Cannot flock $file: $!";
print "Locked by $$, hit enter to exit: ";
<STDIN>;
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If your process is terminated unexpectedly, the OS is responsible for noting that your filehandles are now closed and your locks are ended.

FWIW, Stevens agress with you in Advanced Programming In The Unix Environment.

Of course, YMMV.

Peace,
-McD