assert_redirected_to partial assertion does not work?

Hi,

From the docs I see:
http://api.rubyonrails.org/classes/ActionController/Assertions/ResponseAssertions.html

This match can be partial, such that assert_redirected_to(:controller =>
"weblog") will also match the redirection of redirect_to(:controller =>
"weblog", :action => "show") and so on

But it my case it does not work. As assert_redirected_to(:controller =>
'articles') expects the index action of ArticlesController to be
triggered.

Any idea why I'm getting this behavior?