Using Solaris 10 and a trival Perl script, I can not reproduce the same symptoms. Here is the script;

sleep 120;
[download]

Then to get it started I am running it using the perl command.

# perl -w p.pl
[download]

The output of ptree is doesn't have two perl processes like you are seeing.

624 /sbin/sh
  625 bash --login -o vi
    651 perl -w p.pl
[download]

I realise that we are using different versions of Solaris (you are most likely running Solaris 9) but I don't thin that this would make a difference.

What is happening in your script? Are you using open with a "|" somewhere?