I was reading up on different classes and stumbled over the part of the Errata that one can use "1 Karma per source per test", with each talent being a source, but "discipline" being one source in the vein of "highest bonus counts" at Defence. The provided example is Warrior and Weaponsmith with their 5th Circle Karma ability not stacking.
So it's correct, that Beastmaster 5 (claw shape damage test) also doesn't stack with weaponsmith 5 (damage test with self made weapon), because they all allow Karma for a damage test, even if it's for different reasons?
Next thing regarding stacking Talents:
Why don't Cobra Strike and Air Dance stack?Panda wrote here:
For Swordmaster and Warrior, Acrobatic Strike and Anticipate Blow are technically both options, but it's hard to imagine many characters truly investing in both given they're not compatible (similar to taking both Air Dance and Cobra Strike, unless you don't have a choice).
/edit: I just read the Thief Karma ability again and it is for attack tests, not damage tests, so I edited that part.