How can the DEs not know...

[Tandra]

No: HPFGUIDX 171312

Ok so in the 5th book it seems like the DEs are all shocked when Harry
declares that their beloved leader is a half-blood himself at the MoM.
That seems odd to me because by then shouldn't they have figured it out?

When they met him at Hogwarts wouldn't they have know there was no
pure blood Riddle family? (the same thing goes for Snape....wouldn't
they have known he was a half-blood too?) But granted there has to be
A LOT of half-blood DEs no? I mean there are only but a few
pure-bloods left.

OK, so back on topic, if they didn't figure it out when he was at
Hogwarts, what about during the time in the Cemetery in GoF? He
mentioned that Harry was standing on the grave of his muggle father
no? Why did no one raise and eyebrow then? So, why is it in OoTP, they
all act appalled and like they had no clue he wasn't a pure blood?
I've babbled on long enough...

TKJ :-)