I just added a new page to my demo site - I selected to use Templates with Editable Regions - Simple Text. I then clicked Clone as ad hoc template - and went to the design view.

Firstly I'm finding that sometimes on clicking on Properties I don't get the left hand menu nav that typically appeares on the page (in IE7). Sometimes its showing but mostly not.

Secondly when I click on design - I can't add any webparts to my page. Other pages if I click on the design tab - it has the editable regions. Even changing the template back to simple text isn't making any difference in my ability to play around with the template. I had original tried Empty template as I just sort of wanted a clean slate - but couldn't see a way of changing the design.

I'm logged in as an administrator - and was able to create a page easily enough earlier today and create as ad hoc - to make changes to the design - so I have no clue why I can't seem to do such a basic thing. I have also tested in Firefox.