When?
I tried it 2 days ago with sheep (Parry only, no bushido, used a buckler). Attacked 9 sheeps and tabbed out of combat. They came running towards me and and stood around me, but were only attacking me every 10 seconds a single time. It was wierd. Took me ages to get a few gains (started from 100.0).
After an hour I got so bored, that I decided to switch to skeletons. They took me from roughly 100.5 to 109.0 within another hour. At 109 I stopped gaining. So I recalled back, took a crystal ball of knowledge and went back to the very same skeletons. The crystal ball reported "too easy" for parrying, which means I can't gain off them.
Maybe something has changed with a patch after the last time you all trained parry?
Haven't tested the sheeps with the CBoK, but will do that, the next time I'm logged in. But TBH, I don't expect, that sheeps give any better gains than skeletons...