This isn't a bug ... but might be a compile issue on Jboss distribution. Looks like Jetty has RELEASE_MAJOR_MINOR in the UserAgent field. I would think it is intended to be Jetty/x.x instead. Maybe something isn't getting filtered on the build?
18:15:12,171 INFO [HTTP] HTTP response headers for http://localhost:8080/test/index.jsp
Servlet-Engine: Jetty/RELEASE_MAJOR_MINOR (Servlet 2.3; JSP 1.2; java 1.4.1-rc)
Date: Thu, 12 Sep 2002 22:15:12 GMT
Server: Jetty/RELEASE_MAJOR_MINOR (Windows 2000 5.0 x86)
My fault - it is already fixed in CVS.