I think the other replies probably have it nailed, but I've encountered issues before writing my own forking script (it was also on Solaris, though I don't know if that made a difference).

I spent what seemed like weeks tracking down all of the places where it could go wrong, and leave zombies or just "hang" waiting on children. Finally I came up with the code in Re: Concurrent Processes, and never had any problems (at least, not on Solaris).