The newly "Added: Meeting requests from email messages are now automatically added to a user's calendar in webmail with a tentative status." is not showing any sort of tentative status. When one checks availability from the meeting invite email it shows the meeting as a normal meeting, not tentative status, so it looks like one already has a meeting at that time. Most people will decline the meeting since they think they already have a meeting at that time. The meeting email gets sent to the deleted folder, removing the ability to accept the meeting and the individual is removed from the meeting on the calendar.
I don't know who at SmarterTools thought this was a good idea but I would suggest that they test their new ideas before releasing them!!!