I just got the mercenaries exp, so I've only just noticed this 'bug' now.
(Versus godlike AI) The Torians will sometimes inexplicably declare war on every major faction simultaneously. This happened even when they weren't the strongest, and when I had excellent relations with them. The buggy part was when there was no window or indication that we were at war (No 'die you vermin message'), I only noticed when they started blowing up my starbases.
I assume that it could be an event or something, but it has happened twice now and only with them.