it's even worse:

salva@tokio:/tmp$ perl bug.pl 
running "ls -al" (pid = 25963) ... 
closing ... 
cannot close: No child processes -1 at bug.pl line 17.
[download]

But when I launch the script with strace to see what's happening at the OS level...

salva@tokio:/tmp$ strace -f -o /tmp/out perl bug.pl 
running "ls -al" (pid = 25984) ... 
closing ... 
total 358
drwxrwxrwt 11 root  root     600 2007-10-16 15:28 .
drwxr-xr-x 24 root  root     736 2007-07-17 11:58 ..
-rw-r--r--  1 salva salva      0 2007-10-16 13:54 bar
-rw-r--r--  1 salva salva    373 2007-10-16 15:28 bug.pl
-rw-r--r--  1 salva salva     26 2007-10-16 13:52 foo
drwx------  3 salva salva     72 2007-10-16 09:21 gconfd-salva
...
[download]

It works!!!

BTW, I am running Debian unstable and perl 5.8.8.