Cookie exceptions are deleted when Tor Browser is closed

I'm trying to log into a website and stay logged in -- I trust the website, just not my ISP. But I don't want to keep cookies around for all sites, just the one. So I set the browser to clear cookies on exit, and added a cookie exception for the website ("Manage Permissions" under Cookies and Site Data).

When I restart the browser, the exception is gone.

This used to work on an older version of Tor Browser; unfortunately I can't remember which update broke it. I'm on v9.0.5, which I believe is the latest stable version as of now.

Trac:
Username: silverwolf