In Sakai 2.9, we've been noticing that pres.end is entered as an event within a few minutes after pres.end even though there is no logout or session ending. I've tracked this down to having the timeout warning dialog enabled and the direct/session endpoint resetting the session, which calls into presence triggering this event.
There was originally a workaround for old versions of jquery on
SAK-16162 which set the date, it looks like removing this stops this behavior. I'm not sure what (if anything else) has changed in the SessionEntityProvider but I'll look at this a little more. It doesn't seem to have any negative impact on the user experience, but if you use these pres.end events for reporting, it isn't very useful.