Very odd, I guess I will merge your suggested fix but I am still bothered by why this is happening. It seems very isolated and the fix only avoids one session_start(), which makes me believe its the root of the problem. With that said, I have no good way to debug and test this, especially without error logs.
I will have your changes merged later today and hope the issue goes away permanently.
Update: I pushed this change out now. Let me know if this helps.