I came across this pair a while ago:

The two stamps are basically the same but appear to be issued from different countries. Depicted are King George and Queen Elizabeth, and judging from the dates given (1923 – 1948), the stamps commemorate the Royal Silver Anniversary. Naively, I wondered if this might be a case of philatelic piracy. Suspicions were dismissed, however, after a quick search; it seems that this a commonwealth-wide issue. You can view other countries’ incarnations here.

On a side note, a source indicated that Swaziland and Seychelles did in fact release a joint issue at one point, in recognition of John Paul II.