This only happened in a 1.5 game (started in 1.4).
I am allied with the Drath.
The Altarians had a diplomatic incident with me (the event) and we went to war.
I totally destroyed their fleet, but because I'm neutral alignment and have always had good relations with the Altarians, I didn't take any of their worlds and accepted a white peace soon after. 2 turns later the Altarians said something to the effect of "Your war with the Drath is unjust, we are declaring war on you" and they did. I took some worlds and again settled for peace. After about 5 turns they still think I'm at war with the Drath and declared war on me again.
I was allied with the Drath throughout this time.