Just tested it, you're right--once the animation reaches a certain point (once it starts lunging towards you), you can't interrupt it. I always thought I had just mis-timed the block.
You can still keep them stunlocked though by interrupting a breath attack with a bash, getting a hit or two in, and backing just out of bite range while they recover. This will cause them to attempt another breath attack... which you can interrupt with another bash and rinse and repeat until they are dead. You will take a half-second or so of breath attack damage if you don't time it right, so make sure you've got some elemental/magic resistance going during the fight.
Just tested it, you're right--once the animation reaches a certain point (once it starts lunging towards you), you can't interrupt it. I always thought I had just mis-timed the block.
You can still keep them stunlocked though by interrupting a breath attack with a bash, getting a hit or two in, and backing just out of bite range while they recover. This will cause them to attempt another breath attack... which you can interrupt with another bash and rinse and repeat until they are dead. You will take a half-second or so of breath attack damage if you don't time it right, so make sure you've got some elemental/magic resistance going during the fight.