What is the mechanism of placelimite order

Hey there:

I've got a problem about the execution of placelimte order, it took about 6 month to fill this order, could anybody give me some explaination. Also, i've set the parameter expire to cancel the order in half an hour, it still did the same.

See the first line, i've place this order at Sep 2012, but it got filled on 2012 Dec (second line), which is really wired.

Thanks

Best