I don't know about the other spec skills, as I don't usually use doubleblock when fighting people that can use them, but

You block Hestafles's attack against Correllia.
Hestafles is covered with bleeding wounds.
Hestafles laces his fingers together and hammers his fists at Correllia!
Hestafles's crushing blow knocks Correllia down!
You block Hestafles's attack against Correllia.

I blocked the damage from Crushing Blow. Can also do this with Pummel. Could be by design, I have a feeling it's not.