[Kameron8]

It appears that Thousand Stab (and I assume some other multihit attacks) benefits from 'Reduce the Effectiveness of Enemy Armor' weapons in unexpected ways. Using a Leporidae Verglas/Demon Hunter with Reaver and Martial Lawbreaker, I was using Raging Thousand Stab with a Rebelling-enchanted Needler fist weapon (This enchanted version replaces the 50% strength + 50% cel scaling with 100% cel). Then, I compared the damage with face stomp's.

Data:

Against the same target with both skills maxed and no charge bonus, the damage came out to be:

Thousand Stab: 134 damage total, only 118 damage if the bonus wind damage is deducted.
Face Stomp: 119 damage total.

The formulas for both skills are Weapon Power + Celerity + a bonus based on rank. Face stomp's bonus is 50 damage, Thousand Stab's is 17. Instead of seeing face stomp deal 33 more damage, we are seeing them deal almost exactly the same damage. When tested with a Shredder Replica, however, Face Stomp began to deal 16 more damage. This hints at 5 armor reduction being applied for 4 instances of Thousand Stab, and 1 of Face Stomp.

To continue tests, I removed the expertise for fist weapons off of the character. From there Thousand Stab began to do even less damage.
No Expertise, With Needler:
Thousand Stab: 113 damage (post wind-damage deduction)
Face Stomp: 119 damage

No Expertise, Shredder Replica:
Thousand Stab: 93 damage (post wind-damage deduction)
Face Stomp: 114 damage

So I can't say for certain what isn't scaling correctly, but Thousand Stab seems to be behaving incorrectly with certain bonuses to damage like Expertise and 'Reduce effectiveness of armor'.