if the POM references a URI like
absolute URLs used in the site.xml file are converted to relative references.
For example a reference to to "http://struts.apache.org/1.x" becomes "1.x", and a reference to
just "http://struts.apache.org" becomes an empty string.
If the documentation is being used offline, there are many cases when we want to refer people back to the website, to be sure the current information is used. The best use case is a download page that determines the mirror via CGI.
Another use case is referring to a sister site in the domain, that might refer to another version. If used locally, the other site might not be in the relative location.
Switching back to beta4 cures the behavior, and absolute URIs remain absolute, as expected.