I didn't mention it, but this web application was running on a Tomcat web server, which didn't seem to recognize ';' as a valid query parameter delimiter. Regardless of the fact the web app was coded in Java, this issue of improper error handling is universal. In fact, I found similar instances in my other Perl web applications as well. ;-)
If you read the W3 standards on this you'll find that & is the incorrect and outdated delimiter and ; is the favoured and the correct option. Nice to know Tomcat keeps up with such standards. :)
As a side note, the CGI.pm module has supported both since the first release.