RSpec, controller testing, and routes.rb

I didn't see any forums or lists for RSpec users, so I'm hoping there
are RSpec users on this list who may be able to help.

I have this in my routes.rb:

map.signup 'signup/:step',
    :controller => 'register',
    :action => 'signup',
    :step => 1

This test in the associated *.rspec file passes:

it "should assign @step to 1 on a get to 1" do
  get 'signup', :step => 1
  assigns[:step].should equal(1)

This one fails:

it "should assign @step to 1 on a get to /signup" do
  get 'signup'
  assigns[:step].should equal(1)

Even though that second test fails, when running under mongrel the
controller does the expected thing. If I GET /signup, the @step
variable (which is simply assigned the value of params[:step] by a
before_filter) is set to 1 appropriately. It seems that the default
:step set in the routes.rb works when running in a server, but not
during testing. I find this odd, since I am able to test my routes
with route_for, and they all pass. It seems that during testing, some
of what routes.rb specifies works, and some doesn't.

Is this to be expected, or have I managed to break something? It's
sort of hard for me to accept that I cannot test behavior of my
controller that relies on mappings in routes.rb, so I'm guessing I've
got something wrong somewhere.