The following URL handles fine under Java Jetty but it seems ASP .NET Web Development server does not like it and errs with a 400 Bad Request

http://localhost:8080/gadgets/js/views:dynamic-height:setprefs:analytics.js?v=de9b113d5936476a4f33d621f31c3&container=default&debug=0

The colon in the URL body (vs. query string) is the cause of the problem. The colon and a few other special characters in the URL body will cause the 400 Bad Request. URLEncoding these special characters does not fix the problem either. Apparently, this is a 'feature' and not a bug as described here.

In the end, I replaced ':' with '__' to seperate the js features.