you can see in this videos that i got stacks when i killed infernus after ult and when i killed infernus with ult, but not if he's killed by tankbuster itself
in recent patch vindicta is getting stacks if enemy die in 4s after ult, but if you kill enemy with tankbuster or mystic burst you will not get any stacks for kill
on the first video I bought lucky shot first and armor piercing second, damage varies in
9 - base damage
22 - armor piercing proc
32 - armor piercing proc with lucky shot
on the second video I bought armor piercing and then lucky shot, damage becomes
9 - base
22 - armor piercing proc
47 - armor...
When you close the shop, there is an invisible cursor that can hover over the quickbuy button preventing the character from shooting
In video character just buy items but in game that prevent shooting
Additionally the cursor might hover over the "hold tab" button on the testing tools panel