JSPX pages are supported.
It may be because of server configuration or a bug.
Please share the server configuration details.

I think this is an issue I have seen before (with the same server you are using).  I think the server does not recognize the useragent string that it is getting from Enterprise Browser.  You can change that string in Enterprise Browser to test this, but what I saw in the past is that if you change it, you are likely to break the Enterprise Browser features (scanner, etc).  I think the eb*.js files look for something in the useragent string to know that the page is running on Windows CE so that the proper EB Objects get loaded.  I think the problem we saw in the past was that the trinidad server does not recognize "Windows CE", so it fails.  Not sure if there is a way to fix this on the server end (so it recognizes "Windows CE", but if so, this would be the right way to fix this.  I think the customer in my case edited our ebapi-modules.js  on his server so that it only checked for "Windows", not "Windows CE".  This worked for him, but not a great solution, since you would need to do it again any time you update that file, and also I'm not sure what will happen when someone loads that page from a regular Windows machine that is not running EB and does not know what to do with the EB objects.