I wrote the wgsi handler, but running it I found:

$ python2.4 wsgi2.py 
workhost.local - - [26/Jun/2009 08:02:43] "GET / HTTP/1.1" 200 5225
Traceback (most recent call last):
  File "/usr/lib/pymodules/python2.4/wsgiref/handlers.py", line 92, in run
    self.result = application(self.environ, self.start_response)
  File "/usr/lib/python2.4/site-packages/roundup/cgi/wsgi_handler.py",
line 58, in __call__
    client.main()
  File "/usr/lib/python2.4/site-packages/roundup/cgi/client.py", line
361, in main
    self.inner_main()
  File "/usr/lib/python2.4/site-packages/roundup/cgi/client.py", line
523, in inner_main
    return self.write_html(self._(error_message))
  File "/usr/lib/python2.4/site-packages/roundup/cgi/client.py", line
1112, in write_html
    self.header()
  File "/usr/lib/python2.4/site-packages/roundup/cgi/client.py", line
1376, in header
    self._socket_op(self.request.start_response, headers, response)
  File "/usr/lib/python2.4/site-packages/roundup/cgi/client.py", line
1081, in _socket_op
    call(*args, **kwargs)
  File "/usr/lib/python2.4/site-packages/roundup/cgi/wsgi_handler.py",
line 70, in start_response
    description), headers)
  File "/usr/lib/pymodules/python2.4/wsgiref/handlers.py", line 185, in
start_response
    assert type(val) is StringType,"Header values must be strings"
AssertionError: Header values must be strings
workhost.local - - [26/Jun/2009 08:02:44] "GET /@@file/style.css
HTTP/1.1" 500 59

The problem is in cgi/client.py

roundup/cgi# diff client.py client.py.orig 
1326c1326
<             self.setHeader("Content-Length", str(length))
---
>             self.setHeader("Content-Length", length)


This is the only header I found sent in a no string format

I forgot: 
Roundup version 1.4.8
There was no problem in the 1.4.6 version

This appears to be a duplicate of issue2550552, which has just been fixed.