Focus of Spirit stacking with STR/DEX buffs - thoughts?

[Juevento]

Interestingly, Focus also seems to stack with the rampage proc from a Thornstinger. You don't get the strength buff but you get the rune effect.

I have noticed that a proc from the Thornstinger does not result in a buff slot being filled when you have focus of spirit up. I want to look into this a little more to confirm my findings but won't be able to get to it until tonight.