There is a neat bit of research over on the Not Learning Cantonese in Hong Kong blog.
The blog author, Eric, saw an ad for a position at the United Nations and was rather startled to find that the ad had a strange pre-requisite: "candidates had to be willing to renounce permanent residence status in any country except the country of their nationality." He looked into it a bit further and discovered that this isn't just a quirk that applies to that position in particular, but is actual UN staffing policy.
Read the post, What Diplomats Think of Diasporas: Tracing the History of an Obscure United Nations Staffing Policy, to learn why this policy was put into place. And, yes, there is a strange twist that has to do with the United States' citizenship-based taxation laws...
I agree with Eric that it is blatant discrimination against the "people who move around." Very odd for an international organization. Very much behind the times. Talk about de-valuing the diasporas and calling into question their loyalty and fitness to represent their countries.