Entries under PathPrefixRoute does not show full url when calling uri_for()

[GoogleCodeExporter]

What steps will reproduce the problem?
1. define a mapping with Route under PathPrefixRoute. ex: 
PathPrefixRoute('someprefix', [Route('/some/path", name="some_path"])
2. call uri_for('some_path')

What is the expected output? What do you see instead?
I expect to see '/someprefix/some/path'. I see '/some/path'

What version of the product are you using? On what operating system?
Webapp2 2.5.1. OS X 10.9.5

Please provide any additional information below.

Original issue reported on code.google.com by a...@striiv.com on 8 Oct 2014 at 12:10