I'm starting to get a lot of complaints about a new behavior in Outlook:
"When I receive a meeting request, that meeting is automatically added to my calendar as Tentative. When I delete the meeting request, the calendar entry should disappear but doesn't. It used to work as expected. What happened and how do I fix it? "
This change in behavior is actually "by design". Beginning with the Outlook 2007 and Outlook 2010 hotfixes from August 2012, Outlook leaves the tentative copy of the associated meeting in the Calendar when the meeting request is deleted. Surprisingly, many of the first complaints came from Outlook 2013 users.
If you want the tentative copy of the meeting automatically removed from the calendar, you need to decline the meeting invitation, not delete it.
If you think the change in behavior is annoying with valid meeting invitations, wait until you get meeting request spam. Declining meeting invitations is good etiquette, but you don't want to decline spam, as it only validates your address.
While you can turn off Outlook's ability to create tentative appointments as the meeting requests arrive, as soon as you select the meeting spam to delete it, the tentative appointment is created.
Most people delete meeting request from the Inbox, but the appointment (and it's reminder) is left on the calendar.
If you are using Conversations in Outlook 2010 or 2013, you can delete the tentative appointment when you delete the meeting request by expanding the conversation and selecting both items before deleting the invitation. Otherwise, you will need to delete it from the calendar.
Select both the meeting request and the appointment, then press Delete.
For more information, see Meeting Request Spam
Deleting a meeting request does not remove the meeting from the Outlook Calendar (MSKB)
Description of the Outlook 2010 hotfix package (Outlook-x-none.msp): August 28, 2012
Description of the Outlook 2007 hotfix package (Outlook-x-none.msp): August 28, 2012