Logging in via https, and then going back to http is default behavior for openacs5.0. I think there is a parameter setting that controls whether or not login occurs via https.
Pointing the browser to an https url (maybe other than /register) should keep the session with an https connection. At least that is the behavior of openacs4.6.3. Openacs5.0 may be different. (Although I have installed 5.0, I don't have it operating at the moment, so cannot check this behavior.)
