Step to reproduce,
- Create a test page
- Chage the page's theme to be User Dashboard.
- Add a Search portlet to the page. Now the portlet is not able to be added.
- Change the public page's theme to be User Dashboard
- Add a new page
- Add a search portlet to the page.
- Change the page's theme to Classic.
- Now there are 2 search portlets on the page and the one in the Layout can't be removed.