Expelliarmus and backfiring

[Carol]

No: HPFGUIDX 184618

Carol earlier:
> > Just a quick note here. The master of Death is not the master of
the Elder Wand but the legitimate owner/master of all three Deathly
Hallows. Harry may have been, briefly, Master of Death while he wore
the Cloak (inherited from James and rightly his), held the
Resurrection Stone (which, unlike DD, he apparently had the right to
use because he wasn't trying to bring his dead loved ones back to
life, only to have their compnany before he joined them), and was
(though he didn't know it yet) master of the Elder Wand, having
disarmed Draco, the previous inadvertent master. 
> 
Potioncat responded:
> <snip> I thought anyone who recognised the Resurrection Stone could
use it--presuming they knew how, or were lucky enough to work it out.
Marvolo just thought it was a family heirloom and didn't know about
its powers.
> 
> DD knew what the stone was and forgot for a moment what the ring
was. It was the ring, not the stone that damaged his hand. I thought
that later he determined it was better to avoid using the stone. In
this case, choosing what was right over what was easy. 
> 
> When Harry uses the stone, he's using it to give himself strength to
carry out his mission.
>
Carol responds:

I'm not so sure that we can differentiate between the ring and the
stone. I think that the ring as a whole (stone and setting) had been
cursed, just as there was no distinction between the clasp and the
opals in the cursed necklace. Touch any part of that necklace and your
bare hands, and you're dead. But the Horcrux seems to have been in the
stone, which is the only part of the ring that was broken by the Sword
of Gryffindor. (Odd. Very odd. The Basilik-venom-emposwered sword
should have passed through the whole ring, which should not have been
wearable. And Dumbledore, who wanted only the stone, should have
removed it from its setting rather than putting on the ring, which
would not bring Ariana back. (He knew that it had to be turned three
times.) 

I still think, though, that he wanted to use it for an unworthy
purpose, to bring back the loved ones, especially Ariana, who had died
through his carelessness, just as the second brother in the tale
wanted to bring back the girl he loved even though she didn't want to
come and her death could not be reversed. Doesn't he say something of
the sort in "King's Cross"--the Elder Wand was the only Hallow that he
had the right to use, as long as he didn't use it to kill? (No time to
check now, but I hope that someone will.)

At any rate, Dumbledore's stupidity in this instance continues to
astonish me. Did he sense a curse but think that the Sword had
destroyed it along with the soul bit? Did he simply not sense the
curse? Did he think that putting on the ring would bring her back, or
was he putting on the ring as a way of claiming the Hallow that he had
just cracked along the line of the wand? ("My precious!") Didn't he
wonder why the ring itself was still intact even though the soul bit
was gone? Some sort of protective spell must have remained, whether it
was the deadly curse or something else. 

Carol, wishing that it all made more sense and that the Elder
Wand/Deathly Hallows subplot weren't so needlessly complicated