Not sure if this a UI bug or the talent does not work.
When hitting an enemy with Warpath, Vengence or basic attack I don’t see an increase of Strength in the character sheet, DPS increase on the tooltip of the skill or the buff icon next to my health globe.
This is should be a UI issue. If you’re noticing your damage numbers or other things actually in-game not getting stronger, then there might be a further issue to investigate.