There are several clauses of non-discrimination in various international human rights instruments: article 3 of the 1951 convention and articles 9 and 26 of the International Covenant on Civil and Political Rights. The issue is the differential treatment upon designation. That's what I'd like to insist, that it's the impact of that designation on established rights that is important.
We also have to remember that the human rights treaties have to be interpreted in a very special manner. They have to be interpreted to the benefit of the persons who are protected. According to the 1969 Vienna convention on interpretation of treaties, treaties have to be interpreted according to their objective and purposes in good faith, according to ordinary meaning and the objective and purpose of the treaty.
Now, by definition, a human rights treaty has its objective and purposes in the protection of the human beings that the treaty deals with, so in that respect the interpretation of the 1951 convention has to be done in favour of the persons the convention itself aims at protecting.