Jolares

Kubik and me worked out a solution that was also applied with
The damage value now applies correctly and the overflow no longer gets multiplied by Tainted Enrage or Unholy Hero or the likes.
Damage was off only if overflow happened to buildings. Damage to Units done remains the same pre and post changes. That should only affect Units with the Stampede ability. like Mo, Bloodhorn, Juggernaut.

This would explain exactly my observations:
BhB: Bloodhorn Buff, factor 2 = +100%
{[(9'900 *BhB - 5'000) *BhB - 5'000] *BhB - 33'333⅓} *BhB = 31733⅓ = 4760 /15 *100
4760 /15 *100 corresponds exactly to the last Comet Catcher with 240 HP remaining.
Thus, yes. Your assuption hits the nail on its head: the Bloodhorn buff gets applied to the overkill damage after damage calculation.
If this assumption is correct, you should be able to hit damage numbers which oneshot even the beffiest of entities with the right setup of course.

some interesting numbers:
game computes that first building is attacked with 9900 DMG which get boosted to 24800 DMG 😮 (total damage done is 0 -> 24800 + 0 -> 14800 overkill 🤦‍♂️)
second building is attacked with 14800 DMG which get boosted to 34600 DMG 😮 (total damage done is 24800 -> 34600 + 14800 -> 24600 overkill 🤦‍♂️)
3rd building is attacked with 24600 DMG which get boosted to 54200 DMG 😮 (total damage done is 0 -> 54200 + 0 -> 44200 overkill 🤦‍♂️)
4rd building is attacked with 44200 DMG which get boosted to 93400 DMG 😮 (total damage done is 0 -> 93400 + 0 -> 83400 overkill 🤦‍♂️)
5rd building (with commander) is attacked with 83400 DMG which get boosted to 30020.002 DMG 😮 (total damage done is 0 -> 30020.002 + 0 -> 20020.002 overkill 🤦‍♂️)
6rd building (with commander) is attacked with 20020.002 DMG which get boosted to 11006.001 DMG 🤔 (total damage done is 0 -> 11006.001 + 0 -> 1006.001 overkill 🤦‍♂️)
in short WTF???
not even clue where to start looking for what is wrong, is there at least one number right? 🤣

Only happens when the innitial target gets destroyed. If the innitial target has >19'800 (>2* 9'900) effectiv HP (a.e. Comet Catcher with Skyelf Commander ~33'333 eHP), then the damage amount applied is correctly. 
However if the initial target is destroyed, I've calculated a total damage of up to ~86'667 damage (see testsetup below, everything gets destroyed). 
It's quite inconsistant. At least too inconsistant for me to grasp what's really happening. Depending on the setup the (buffed) ability deals inconsistant damage values depending on the number of buildings destroyed:
19'800 (none destroyed)
~24'000 (dont remember the setup)
48'093 (3 buildings destroyed)
86'667 (4 buildings destroyed)
Note: There doesn't have to be a relation on # entities killed to the max damage value, this is just my conculusion after a couple of tests.

Well voidstorm also says that it ignores all shields, hence the amii paladin shield does not detect it and nothing gets redistributed.

@Jolares is correct. And the fix "prevented" is perfect.
The clause on Voidstrom "This damage cannot be warded off with the help of damage reducing abilities because it is able to circumvent every buff or protective shield." corretly takes priority over any damage reducing ability. Thus the Amii Paladins die since their ability clause "Amii Paladins will take 100% less damage" gets overruled.
However, the damaging blow should still damage the surrounding enemies due to this clause: "[...] and distribute 100% of the incoming damage equally to hostile units [...]".

but amii paladins reflect is not tied to negated dmg. it just says "distribute 100% of the incoming damage equally to hostile units".
I would agree with you if the wording was "distribute 100% of the PREVENTED incoming damage equally to hostile units"

Hello Skyladies and Skylords,
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