Steps to reproduce:
1. On Firefox (version 36.0), access PlatformUI;
2. Go to "Admin Panel -> Content Types -> Content";
3. Click on "Create a Content Type" at the bottom;
4. Create a content type called Rich Text with Name and a Rich Text field;
5. On "Content -> Content Structure" create a content of the type Rich Text;
6. On the rich text field, position the cursor on the beginning and click delete as if there was any text there, until the "Add Content" plus icon is removed.
This shouldn't happen.