Looking closer to the Pahang Heritage issue, we tend to wonder if its a coincidence or another one of those famous blunder by POS Malaysia. If you are wondering what I'm talking about, please take a good look at the stamps.
Although this is not a cast in stone rule, I truly believe POS Malaysia and the designer should have avoided this kinda controversies. It will definitely add to the bad rapport POS Malaysia is currently building. Agreed that Pahang's flag is black and white but I'm sure there are millions of ways to reflect them on a stamp; not neccessarily with a black border.
Samples of mourning stamps with Black borders: