In at least the "devel" templates distributed with Roundup, 
clicking on the Bugs "Show unassigned" link in the left sidebar,
will show all open issue rather than just unassigned ones if
user is not logged in.

A fix that worked for me, suggested by John Rouillard in   
  http://sourceforge.net/p/roundup/mailman/message/32903744/
and referencing 
  http://sourceforge.net/p/roundup/mailman/message/32893191/
was to give Search privilege to Anonymous users:

schema.py:
----------
 db.security.addPermissionToRole('User', p)
 db.security.addPermissionToRole('Anonymous', p)
+ 
+p = db.security.addPermission(name='Search', klass='user')
+db.security.addPermissionToRole ('Anonymous', p)
 
for cl in ('severity', 'component',
           'version', 'priority', 'status', 'resolution',