Fix issue #1928, thanks to @ejfinneran for a test case

Gemfile.lock

@@ -87,7 +87,7 @@ GEM
     omniauth-openid (1.0.1)
       omniauth (~> 1.0)
       rack-openid (~> 1.3.1)
-    orm_adapter (0.1.0)
+    orm_adapter (0.3.0)
     polyglot (0.3.3)
     rack (1.4.1)
     rack-cache (1.2)

lib/devise/test_helpers.rb

@@ -45,6 +45,7 @@ module Devise
     def sign_in(resource_or_scope, resource=nil)
       scope    ||= Devise::Mapping.find_scope!(resource_or_scope)
       resource ||= resource_or_scope
+      warden.instance_variable_get(:@users).delete(scope)
       warden.session_serializer.store(resource, scope)
     end
 

test/test_helpers_test.rb

@@ -47,6 +47,18 @@ class TestHelpersTest < ActionController::TestCase
     assert_response :success
   end
 
+  test "does not redirect with valid user after failed first attempt" do
+    get :index
+    assert_response :redirect
+
+    user = create_user
+    user.confirm!
+
+    sign_in user
+    get :index
+    assert_response :success
+  end
+
   test "redirects if valid user signed out" do
     user = create_user
     user.confirm!