Correction: This works great in a site I just upgraded to 5.4 that's running on a Linux shared server (HostGator)

The issue is present on a client server, running Windows Server 2003. Perhaps it's just a fluke? Or perhaps the error has something to do with the difference between the servers?

It could be just about anything. You need some tools to check if all of the JavaScript files are being loaded. If not, you need to track down why not. Perhaps there is a permissions problem. Maybe a JavaScript file is missing or named incorrectly. Put your detective hat on and dig in.