Cannot break alliance with pirates

I played game during which at the end I planed to destroy all minor factions. Everything was working fine until last one - Pirates.

Despite bar on button to break alliance drops to zero nothing happens. Pirates are still friendly.

Screen with mentioned button with empty bar

Upon request I can provide save.

 

Edit:

Someone on Discord informed me that it can be because of "Truce Among Rogues" research. Dunno if that's the design or is it bug.