Oddly enough, the BBC News site ran a feature on a case of this sort earlier this week. It concerns a Chinese soldier, Wang Qi, who has been prevented from leaving India (though not formally imprisoned) ever since the Indo-Chinese war of 1963. I've made a fairly detailed study of cases of long imprisonment, and this is by some distance the most unusual such case that I have come across to date.

In the aftermath of the Second World War, the USSR held onto more than a million German, Japanese and German allied POWs for up to a decade, many of whom died while still incarcerated; in one case that I know of, a former Japanese PoW named Uwano Ishinosuke remained living in the USSR, and then Russia, as late as 2006, having never returned to Japan; he had been held captive in a Russian camp until 1958.

The position of German soldiers in the gulags is still a pretty hot political topic in some circles, and a lot of the most accessible online sources are highly dubious ones hosted on far right websites – so, as is not my area of expertise, I'm hoping a better-informed contributor can supply some details in due course.