The same thing has been happening here off and on for the last week or so.
I'll select all the orders on the Awaiting Shipment list, mark them shipped, receive confirmation only to find 1 or 2 still sitting there awaiting shipment. After a bit I realized the system was running slow, if I wait a few moments with the awaiting shipment page still open, then refresh the page the slow pokes move over to the shipped list. The first time it happened I didn't know what was going on either.
Leaving multiple feedbacks has been behaving sort of like that too, there's a considerable delay before the feedback left icon appears in the listing info.