Shoulder "rune" Southpaw doesn't stack with regular set bonus

[shaugen]

Describe the bug
It doesn't seem like the Shoulder Rune called Southpaw (-2sec cd on Shield Slam) stacks with Vindicator's Battlegear 3 set bonus, unfortunately.
This works on the current PTR, so I assume it is intended to stack.

To Reproduce
Load the linked setup and click simulate.
Check results, timeline.

Expected behavior
Shield slam is cast ever 4 secs, and not every 2 sec like expected

Sim Links and Screenshots
(https://wowsims.github.io/sod/tank_warrior/#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)