When you guys created flail&shield, you reused the regular flail’s attacks but shuffled the attacks around a bit. This much is obvious from the animations and damage profiles for both weapons (The regular flail’s light attacks 1&2 became the Flail & Shield light attacks 4&5, and the regular flail light attacks 3&4 became the Flail&Shield light attacks 1&2.):
But when you guys moved the attack profiles around, you forgot to also move the tank property: thus the regular flail’s light attack 1&2 damage profiles became the damage profiles for the Flail & Shield light attacks 4&5 except for the Tank modifier which remained on the Flail & Shield light attacks 1&2 which I assume is probably an error since Flail & Shield light attacks 1&2 are single target overhead attacks with the lowest damage and stagger cleave limit values a weapon can have (2,24) thus them having the tank property is utterly pointless.
TL/DR
The flail & shield light attack 1&2 shouldn’t have the tank property, the fact that they do is probably a remnant of the copy-paste from the regular flail’s attack profiles. The Flail & Shield light attacks 1&2 should lose the Tank property, which should be on the Flail&Shield light attacks 4 & 5.
Edit: The Skull-splitter & Blessed tome light attacks also have the tank property even though they’re -just like the Flail&Shield light attacks 1&2- single target overhead attacks with damage and stagger cleave limit values of 2,24.
So is it also an oversight or is there more to the tank property than the mass modifier effect? It makes sense to have a property like tank on the attacks like the regular flail light attacks 1 and 2 which are designed to cleave through several enemies but for the flail&shield light attacks 1&2 and the Skullsplitter&blessed tome light attacks not really (unless there’s more to the tank property).