Maybe you have already noticed it but when you use Shield Block you dont gain 100% more BV. I have tried it out on several bosses and checked it in the character panel. You do however gain 100% more BV for one attack with the Critical Block talent. I wrote a ticket about it and told them I didn't think it was working as intended, but after a few hours with no reply I had to log out and I got a long pointless mail(as you usually do) where they said they hadn't noticed anything.
So today i decided to found out how it was working and I found out that Shield Mastery(30% more BV) is not applied on teh bonus BV from SB. So this is how SB works atm.
Lets say my BV 542 and I have the Shield Mastery talent. My BV from gear is 313(without talents) and my BV from str is 104. (313+104)*1.3 = 542.
That should boost BV to 542*2 = 1084 when you use SB. But as the formula is now you get your BV+BV from gear(without talents)+BV from str(without talents) = 542+313+104 = 959.
I might be mistaken and SB is supposed to work this way, but it seems weird to me. SB should be working as intended without Shield Mastery.(assuming my formula is correct)