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.
I have to agree they surprisingly look good but a black border is definitely very disturbing. Black border stamps are often associated with "national bereavement" or more commonly called "mourning" stamps. OMG, this is definitely a big blunder if you ask me.
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:

The Greek 250-drachma-on-3d stamp (Scott 499) shown in the stamp above was issued as a memorial for King George II, who died on April 1, 1947. The stamp was surcharged with a new value and overprinted with black borders. Overprinting existing stamp stocks allowed a quick release of the mourning stamp, just 14 days later on April 15.

Those in mourning used letter paper and envelopes that were edged in black. Some sources say that the width of the borders varied from narrow to broad based upon the closeness of the relationship of the writer to the deceased, the amount of time that has passed, or the importance of the deceased. The cover above illustrates a mourning cover mailed from Chelsea, England, to Yonkers, N.Y., in 1937.

The use of black borders was not restricted to postage stamps. In 1935, Belgium used black borders on semipostal stamps depicting the lovely Queen Astrid. Astrid was a Swedish princess who married Belgium's Crown Prince Leopold in 1926. In 1934, he ascended the throne and Astrid became the queen consort. On Aug. 29, 1935, 29-year-old Queen Astrid died in an automobile accident in the Swiss Alps. Just two months later, on Oct. 31, Belgium issued the 70-centime+5c Queen Astrid semipostal stamp (Scott B174) shown in stamp above. It was the first of a set of eight black-bordered Queen Astrid semipostal stamps.