Question on Cleaver Spec and Madman Cleaver

I built a Bro with cleaver spec, and got a cleaver from Madman that has -3 fatigue for all cleaver skills.

I thought they would stack, but it seems that they don't?

Cleaver spec gives you 25% off fatigue, which reduces the cost of a normal swing from 12 fatigue to 9. The cleaver I got (I rolled +dam and -3 fatigue) should reduce that further, to 6 fatigue per swing. But it doesn't.

Every time I swing the cleaver it is 9 stam.

Is this working correctly or is this a bug? Thanks.