getRequestURI returns welcome file instead of original request

Given a request to / and a welcome file set to /index

JBossWeb wil return "/" when HttpServletRequest#getRequestURI is called,
and "/index" when HttpServletRequest#getServletPath is called.

Undertow will return "/index" in both cases.

It's clear what happens by looking at ServletInitialHandler#handleRequest
which does a full rewrite for welcome files:

exchange.setRelativePath(exchange.getRelativePath() + info.getRewriteLocation());
exchange.setRequestURI(exchange.getRequestURI() + info.getRewriteLocation());
exchange.setRequestPath(exchange.getRequestPath() + info.getRewriteLocation());

The Servlet spec (10.10) does seem to justify this somewhat by saying the
following:

The container may send the request to the welcome resource with a forward, a redirect, or a container specific mechanism that is indistinguishable from a direct request.

However, the JavaDoc for HttpServletRequest#getRequestURI doesn't seem to allow this.

Example:

With a welcome file declaration in web.xml as follows:

<welcome-file-list>
    <welcome-file>index</welcome-file>
</welcome-file-list>

and when requesting the context root of an application (e.g. http://localhost:8080 for a root deployment), the results are as follows: