1. How could the cup get to the potion? Dumbledore must have known how to get past the barrier then.
2. How come Harry couldnt get water into the cup? It kept vanishing...
It dosen't make sense... Why would Dumbledore's newly conjured cup not contain water? If he knew how to let it contain the potion, surely it could contain be able to contain water! Unless Dumbledore wanted to drink the potion and make Harry almost kill them both by disrupting the Inferi... But then why would Dumbledore even come for the fake locket, unless he thought it was real. But that still dosent explain why it couldnt contain water.
And... Why did Dumbledore keep his memory in a vial instead of conjuring it, like he did all the other times... It makes me think that it wasnt Dumbledore... Maybe his brother Aberforth...

This bit leaves me no choice but to believe that R.A.B. is Regulus Black.
In the Denmark(i think it was) series, the Blacks are not "Blacks"...
But "Zwarts" Coincedentally, the HPB in Denmark's R.A.B. is not R.A.B., but R.A.Z... Tell me thats coincidence.