Tankbuster not triggering max health bonus?

[makosmusicbox]

With Mo and Krill, I've tested in the sandbox on dummies with half health on myself, full on myself, neither seemed to change any damage. Doesn't seem to be applying % on a full health dummy (Burrow + improved spirit 2 and Tankbuster). Also, how does this work? Is the max health bonus % based on ME having max health or THEM having max health? Did I overlook something or is this truly a bug?

 

[Cyclespx]

don't think burrow will proc tankbuster, it needs to do 165 in a single hit
burrow hits multiple times for its damage

but it'll do damage based on the target's max health, their and your current health doesnt matter