Integration test receives HTTP 200 response when it should be a redirect

This is probably due to my novice understanding of integration tests,
but this behavior looked pretty strange, so I figured I'd ask.

The application I'm working on at present requires users, upon login,
to assign themselves to a location. Locations are pre-loaded in the
database. Because I don't want the user "getting around" this
functionality by ignoring it and just clicking something else (this is
a workplace-only application), I'm using this as part of my
authentication process.

Long story short, every controller has a before_filter called
"login_required". The login_required method exists in
ApplicationController. It's very simple: checks to see if the user's
session contains a "username" value. If not, they're kicked back to
the authenticate controller and told to login.

If they DO have this in their session, however, is where the fun
starts. At that point, it looks for the user in the database
(original authentication is done by Active Directory, and I have a
local database that "syncs" with AD nightly). If found, it then
checks to see if the user's home location (called a "store" in this
case) is set. If NOT, it redirects them to /users/assign_location.

And there's the rub: it's an actual call to redirect_to. Yet my
integration test receives a 200 response (success), which of course
causes assert_redirected_to to fail.

Here's my before_filter method that's being called (what's responsible
for said redirect):

class ApplicationController < ActionController::Base
  # ...snip ...

  def login_required
    if session[:username]
      # Has this user set his/her home location yet?
      begin
        @user = User.find(:first, :conditions => {:account_username =>
session[:username]})
      rescue ActiveRecord::RecordNotFound => e
        logger.warn "Couldn't find user with account_username #{session
[:username]} - AR threw #{e}"
        reset_session
        redirect_to :controller => "authenticate", :action => "index"
        return false
      end

      if !@user.has_home_location?
        # Do the redirect
        redirect_to :controller => "users", :action =>
"assign_location"
      end

      return true
    end

    flash[:warning] = "Please login to continue."
    session[:return_to] = request.request_uri
    redirect_to :controller => "authenticate"
    return false
  end

I have an integration test that just tries to do a straight get
request on a particular URL. For example:

    get "/users/"
    assert_response :redirect
    assert_redirected_to "/users/assign_location"

In this test, the session is totally blank. It doesn't exist yet.
So, by default, the user should be redirected to /users/
assign_location. However, my tests report that the server responds
with code 200:

  1) Failure:
test_user_assings_own_location(UserFlowsTest) [/test/integration/
user_flows_test.rb:24]:
Expected response to be a <:redirect>, but was <200>

Any thoughts as to what I'm doing wrong here?

And another thing I forgot to mention:

I fired up script/server to see if it was ACTUALLY redirecting, and it
sure is. Using Firebug (Firefox extension) under Firefox 3.5, I can
see:

Location http://localhost:3000/users/assign_location

So it's definitely throwing a redirect, but I have no clue why the
tests won't "see it" as one.