Related Questions:
Does updating my Booking Status to Lost automatically Archive it?
How do I archive all of my Lost Bookings?
Answer:
When you change your Booking Status to Lost there is a "Archive after status change" box already highlighted.
If you don't want this to happen, you will need to uncheck that box before hitting Submit to update the new status.
To Archive all of your Lost Bookings at once see this article on Batch Updating Bookings Status.
