For a number of reasons, treaties about rights after the Universal Declaration of Human Rights tended to be formed along two tracks, the political rights track being treated distinctly from the social and economic rights track. This was often felt to be unsatisfactory, and this led to the Vienna Declaration (1993), which stated,
All human rights are universal, indivisible and interdependent, and interrelated. The international community must treat human rights globally in a fair and equal manner, on the same footing, and with the same emphasis. While the significance of national and regional particularities and various historical, cultural and religious backgrounds must be borne in mind, it is the duty of States, regardless of their political, economic and cultural systems, to promote and protect all human rights and fundamental freedoms.
Note what is not argued here. The theoretical claim is not that all human rights are equally important, but that human rights are interdependent and can't be divided from each other. Unlike more recent garblings, this idea is entirely standard, and is consistent with the possibility that some human rights are nonetheless more central. The Declaration does state that they should be treated "in a fair and equal manner, on the same footing, and with the same emphasis", but this is quite clearly a practical guideline intended to reject the notion that states can pick and choose -- which rejection is something that follows from the notion of 'human right' itself. A major motivation for this was to rejoin the two tracks of international handling of rights.
What seems clear is that certain people have since made certain assumptions about this that are not warranted:
(1) that this is a general feature of international law concerning human rights rather than a relatively new element intended to address a relatively narrow range of specific problems;
(2) that the statement of equality was a matter of theoretical principle rather than a practical requirement about what the international community and the states making it up must do in order to recognize the interdependence of human rights;
(3) that the claim is a statement about the equality of all specific rights rather than, as it actually was in historical context, about the equality of kinds of rights, which, because they had been split in actual practice, had sometimes been treated as optional extras (a salient feature of the Vienna Declaration is its repeated insistence on the protection of all human rights, or as it states elsewhere, "non-selectivity of the consideration of human rights issues").
This has led people to confuse 'all human rights are equally to be treated as human rights', which is the effective meaning of the Vienna Declaration, with 'all human rights are equal', which is an aberration and (as I have said before) gibberish, since it would require at least three falsehoods so serious that it's difficult to conceive what it would mean for them to be true: (1) that human personhood is 'flat' rather than structured so that all human rights are possessed in exactly the same way; and (2) that no human rights have logical or ethical dependency on any other rights; and (3) that all human rights deal with matters of equal inherent value.