Brunei Stamp Postmarked Limbang

By the time you read this, this item will be in someone's hands. I have bid for it on ebay but the price has gone beyond my financial limit. It was US$227, way above the US$150 max I put on it. Why is this valuable?

Firstly, this is a Brunei stamp overprinted during the Japanese occupation of the country. That makes a used stamp expensive. Think of how many Bruneians sending letters in those days. Secondly, this was postmarked Limbang. Limbang, as you know, is currently a part of Malaysia and had been a part of Sarawak ever since it was forcefully taken away from Brunei in 1890. For a Brunei stamp to be postmarked in Limbang is almost impossible except during the Japanese occupation when they treated all the British Borneo territories as one prefecture. And that's why the 4 cent stamp could exceed US$300 by the time you read this.