Warlord's mark + Ruthless Support bugged?

Hi...
Ruthless support has base stun duration of 0.8s
For some reason Ruthless blow doesn't count as stunned and by doing so it dosen't trigger Warlord's mark Rage generation.
Other hit's that stun trigger the rage generation normally.
Tested on multiple strike skills.

Is this intended working mechanic for the Ruthless support?

It should work fine, Ruthless just overrides base stun duration but doesn't guarantee a stun. Do you know for sure which attack is Ruthless Blow? It may be hard to determine considering there's no a counter or smth. So you see a stun effect over the marked monster but rage doesn't generate?
A video with tests would be helpful.

Were you perchance trying to test this in a map with the "Monsters cannot be stunned" modifier?

Seems like monster which tested on had some mod that didn't make over stun threshold value seems to work now...

Was testing idea of warlords mark + boss stunning for permanent berserk uptime.