If you throw the bombs at empty ground, everything behaves normally. But if you throw them at any target, Ulzuin’s Chosen can be triggered with no limit, effectively turning the bombs into no‑cooldown skills.
That said, even with a truly no‑CD Canister Bomb, the damage in the current patch isn’t particularly explosive (though I do acknowledge you’ve already given this set plenty of love). So, if you decide to fix this bug, maybe consider giving the set a bit more strengthening as well?