I've just been using the same code for my own project, and what you have there works for me, so I can't suggest a positive solution. I know this doesn't help! Does the html that your cgi creates on the fly look the same as the static html that works? Or
(1) Do you need to specifiy -language=>'JavaScript'? ... answer probably not, as in the current version of CGI.pm that is the default anyway.
(2) Do you need -onload=>'your.function()' to run the js?

Apart from that I can't think of anything helpful except to repeat that what you're trying to do does work, so there is a solution. Only I don't know it!

§ George Sherston