Every patch seems to affect this passive. Sometimes it even updates with small bi-weekly updates.
For a while it didn't work if you didn't have an skills from the skill line equipped. Then it only worked if you had the skills equipped on the bar you were performing the attack on. Then it went back to working all of the time as long as you have the skill line. It's not surprise to me that it has changed again and at this point I can't even tell you what the actual developer-intended way for it to work is supposed to be.
EDIT: Long-story-short. Don't even bother relying on this passive. Do what everyone else does and use scribing or a standard skill to proc off-balance. This passive is not even remotely useful.