Yeah it’s broken. It only changes the MRU files in memory, not the settings file.
You can go into the GH settings folder (File menu -> Special Folders -> Settings Folder) and then delete the
grasshopper_mru.xml file. Do this while Rhino isn’t running.
Or, to force the MRU list to be written to the disk, you can also open or save a single file after you erase the files via the Preferences.
Works. Thank you very much!