Session login is is unique between logins, but will be reused by the same user.  I've no doubt that there are two attempts to update the same record.  That is because session login is used to validate the user has permission to write the record they are attempting to.  In the scenario described, the user will be iterating through a javascript object on the client browser answering a series of questions.  When they answer, that answer will be persisted to the Db,