I just noticed this started happening today only, but when you click the prefix (Tagged / Installed / Uninstalled) in any area other than inside of the modification thread itself, it takes you to the No Permission page.
For example, when I navigate to User CP > Downloaded Modifications, and click on the Downloaded prefix, it takes me to a no permission page. Previously, it would allow you to mark as Installed or Uninstalled. Same thing with the Installed and Updated prefixes, and this is on all pages, except for inside the modification thread itself. You can click on Mark as Installed and Tag Modification and it behaves as it should.