i have not been running the bst with my group lately, but i did some last night and found this still happens. i tend to run in vorpal mode, but after reading through some of comments (like this one), i tried changing the mode and whatnot... same thing in each mode
i have symbol of celerity blocked on the pet, but he will still non stop chain cast Ally's unity.
EDIT**
So i was testing something... it's somewhere in how it reads which classes to buff... i did single target Sham Unity for haste on sham/cler/ench and other classes' pets. bst did not cast Ally's Unity. BUT, if i cast sham unity on SK,Bard,Zerk,Bst,Rog,Rng,Mnk, the bst would instantly start casting again.