In working with a colleague, we came across what appears to be a bug within Outlook relating to meetings disappearing from calendars after an update is sent. This has been confirmed to affect Outlook 2007 but it may affect other versions as well.
Symptom: A meeting for which you are the owner/organizer disappears from your calendar after sending an update to all attendees if the meeting request was sent to a distribution list or group of which you are a member. The meeting does not disappear if you are explicitly in the attendee list.
Workaround: Before sending a meeting request to a distribution list or group, expand the membership by clicking the “plus” sign next to the name. Once you see all of the members expanded, you may send the meeting request or remove yourself from the attendee list so that future updates will not fall victim to this bug. I would recommend that you remove yourself entirely as an attendee in case other issues arise as a result.
We are unclear as to whether Microsoft is aware of this bug or has a fix in development. Hopefully the above workaround will help some of you that are experiencing this problem.