I've used the 'buy it now' function with my own ID and the item 
has ended. Perhaps in the case of multiple items being listed 
(a 'dutch' auction) the listing continues onward, but in 
unique items I've had my auction close just fine ^^

The 
Yahoo help pages on the topic seem to coincide with this ... I'm 
not fluent, so perhaps someone who is can look it up.