No Option to Minimize TOC Dropdown

In my Settings on a new site, I have checked “Posts” under Enable Support and Auto Insert. I have also checked “Initial View – Initially hide the table of contents” and saved the settings. For some reason, the button to minimize the TOC is missing in the TOC box (I have used this plugin many times before, without a problem) so I cannot minimize the TOC. I have deactivated my other plugins to test for a plugin clash but there was no change. What can be wrong?

The page I need help with: [log in to see the link]