Whirlpooling is actually enough to get the priming solution mixed up.
The issue here is that they have been sitting for over 6 months and they have probably been subjected to big swings in temperature. Not only that but it could just be the long-delayed result of an infection. A very very minor infection that would go unnoticeable could easily take that long to show effects (i.e. overcarbonation/bombs)
I have yet to get a bomb and that's even with some barleywines that I've let sit for over two years, some of which will probably sit a lot longer.
Primary: air and sadness =(
Kegged: air and sadness =(
Bottled: English Barleywine (brewed 9/26/09 -- bottled 5/5/10)
LET'S GO LA!
PLAY FOR GLORY, THE GLORY LA!