As a public service, I pass along some info from today's work activities.
I have discovered that something has changed everyone's Outlook calendar settings (in our organization, at least, some recent update perhaps?), without permission.
If you organize meetings using Outlook, you need to check and/or correct your settings, here is how..
In the Main outlook window, go to
Tools | Options
Then click on Calendar Options, and uncheck "Allow attendees to propose new times for meetings you organize"
Once this is unchecked, you can OK your way back out, and all new meetings should be safe from proposed changes (which have the un-intended consequence of wiping out the original meeting request, and any attachments or history included with them).
I have not found the exact cause of this change, and will continue to investigate, to prevent its recurrence.