diff --git a/tracks/app/models/todo.rb b/tracks/app/models/todo.rb
index feab3068..c3754e53 100644
--- a/tracks/app/models/todo.rb
+++ b/tracks/app/models/todo.rb
@@ -8,7 +8,9 @@ class Todo < ActiveRecord::Base
   
   acts_as_state_machine :initial => :active, :column => 'state'
   
-  state :active, :enter => Proc.new { |t| t[:show_from] = nil }
+  # when entering active state, also remove completed_at date. 
+  # Looks like :exit of state completed is not run, see #679
+  state :active, :enter => Proc.new { |t| t[:show_from], t.completed_at = nil, nil }
   state :project_hidden
   state :completed, :enter => Proc.new { |t| t.completed_at = Time.now.utc }, :exit => Proc.new { |t| t.completed_at = nil }
   state :deferred
diff --git a/tracks/test/unit/todo_test.rb b/tracks/test/unit/todo_test.rb
index 9288cd16..cfb05eca 100644
--- a/tracks/test/unit/todo_test.rb
+++ b/tracks/test/unit/todo_test.rb
@@ -31,6 +31,15 @@ class TodoTest < Test::Rails::TestCase
     assert_not_nil @completed.completed_at
   end
   
+  def test_completed_at_cleared_after_toggle_to_active
+    assert_kind_of Todo, @completed
+    assert @completed.completed?
+    @completed.toggle_completion!
+    assert @completed.active?
+    assert_nil @completed.completed_at
+  end
+  
+  
   # Validation tests
   #
   def test_validate_presence_of_description