Bug Report: Can't log in from profile page

Steps to reproduce:
1. Load site with sample data populated.
2. Log in as sample / sosecret
3. Click on a username (e.g. AS) in a bloom shown in the timeline
4. Click logout
5. Log in as sample / sosecret

Expect to see: A logged in view of AS's profile, with a "Logout" button in the top-right.

Actually see: A 501 error page saying "Server does not support this operation."