Steps to reproduce this Bug:
1. Create a webtest inside a template, with one simple step
2. Create a diagram inside the same template, with "Response time for step ..." as data source.
3. Deactivate the complete webtest in the template configuration screen
4. Reactivate the webtest in the configuration screen
5. Now some data-elements in the webtest are still deactivated.
You can see this, when you try to create another diagram with the webtest as data-source. The screenshot shows this.
I found no way to get this elements back to active without creating a complete new webtest.