If I buy out an item and it won't show up in my "completed" tab, when I immediately purchase another item (I usually filter for items selling for 100g) the new purchase will force the original item to populate on my "completed" tab.
The long version:
I am experiencing a reoccurring problem since at least 3/31/13 where I utilize the "buyout" function, and the purchased item does not show up on my "completed" tab. If I do not use the above work around, the item will not show up until the original auction period expires. There has been at least one occasion where intermediate purchases did not terminate this bogus waiting period.
Frequently I will go from the tab where I bought the item, to the completed tab, and the newly purchased item (just 10 minutes ago a stack of rubies) is very briefly showing in the list of completed items, only to immediately vanish.
I do not know what is causing this bug, and it is intermittent, but common for me.