I speculate that there may be a problem in which OpenID implementations hash URLs, and these change when an s is added to the scheme. However this is pure speculation, I don't know much about OpenID yet.
Here is a specific example of new MyOpenID breakage with latest 2.0.1 release:
Go to Toodledo.com, select login, then login using OpenID, on next screen enter a MyOpenID.com user name (make one up like xyz.MyOpenID.com or create one for yourself) & submit. You will receive a "Bad Redirect" error message at MyOpenID.com. Disabling the MyOpenID.com rule allows the login to work properly again. As I said, this just broke with the latest HTTPS Everywhere update!
If you need to contact me for clarification/screenshots/whatever, you can do so at SESmith2112 /at/ gmail dawt com.
Interesting. We probably need the fix (at a recommended-UI or specification level) to come from OpenID, then. How numerous and how independent are the deployed OpenID implementations?
I'll send a note to the OpenID Foundation and see if they can advise us about this.