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human
[Harry Potter] What were the mechanics that prevented an Elder Wand wielding Albus Dumbledore from lifting the curse placed on the Defence Against the Dark Arts job by Voldemort?

My immediate thought is that the original caster of a spell has an advantage or 'ownership' over it compared with some randomer trying to lift it.

This doesn't seem to be the case for all spells though.  For example, when Fake Moody turns Malfoy into a ferret, McGonagall turns up and undoes the spell with ease.

What's different with Voldemort's curse on the DADA position?

My thoughts:

* It can't *just* be to do with outright power. You could make an argument that Voldemort's more powerful than Dumbledore, but giving Dumbledore the Elder Wand would surely tip it in his favour.

* The curse itself presumably wasn't completely unliftable as it was broken when Voldemort died.  So it wasn't just a permanent change, unalterable by anyone.

* What exactly was the curse cast *on*?. We know its effects, but cursing a job is essentially cursing an abstract concept. How did Voldemort do this and how would Dumbledore go about undoing it?

The best explanation I can think of is that Voldemort basically had the 'password' to that curse and that Dumbledore (even with the Elder Wand) was unable to 'hack' it.

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edit: This is all under the assumption that Dumbledore actually wanted the curse gone. I think it's safe enough to say he did, given all the trouble it caused him finding new teachers, and the fact it resulted in deaths, memory losses and everything to do with Umbridge.
gpt
I think this curse was more of an urban legend in the school. 

Quirrel didn't want to stay there more than one year anyway - the job was a disguise. Lockhart was so incompetent that the only reason they took him was that there were no other applications. Lupin stated himself that he only wanted to stay one year IIRC. 

Of course one could just blame a curse for all this, but that would be rather childish.