As untyped bonuses from the same source, they wouldn't stack. The confusing nature of the feat, of course, is why that Special clause tongue-in-cheekly refers to the fact that the designer really needs to specify what happens if you take it multiple times.
But then this means that both the feat *and* the Attribute is the source.
This ruling bothers me a lot. I feel that this makes it hard to figure out what feats/abilities actually do by reading them. Cause now you have to keep in mind how that feat calculates its numbers. It just feels to me that it is needlessly constraining future design space. The bonus type-system is elegant and intuitive. You can tell what stacks and what does not just by reading a feat or ability. Making attributes sources means that you need to back track where modifiers come from.
A specific example is of Fury's Fall, where whether that feat does anything at all is dependent on if I have Agile Maneuvers or not. And that means that when I take Agile Maneuvers I need to now note on my sheet that my attack bonus now has a dex component.