Cucumber scenarios don't run when is task invoked in a lib/tasks task

I have the following task in lib/tasks:

    task :cuke_test_db_constraints do
      puts 'cuke_test_db_constraints'
      ENV['TEST_DB_CONSTRAINTS'] = '1'
      Rake::Task['cucumber'].reenable
      Rake::Task['cucumber'].invoke
    end

    task :default => :cuke_test_db_constraints

As you see, I want to run cucumber again after setting an env variable. However, while cuke_test_db_constraints task runs, cucumber doesn't run scenarios. The cucumber task itself runs, I checked it with adding debug output under :cucumber task in lib/tasks/cucumber.rake.

Any ideas? Thanks.