Temporary registration rewards
Temporary registration rewards are those objects that are obtained via registration specials. They could be portable holes, or greasy aprons, or slippers of questionable sexiness.
These registration rewards, being temporary, have an expiration to them. You may, at any time, review the date at which such items will expire via the OOC command. Threshold has a daily routine to check at 6AM ET for those expirations and remove those expired objects from the game.
If one of those items is a container, you should probably have emptied it of its contents ahead of time. Who knows what may happen to treasure that was contained within at the time the expired object is removed?