Are United Planets ceasefires working at all?

In two games I've had the United Planets vote on a ceasefire to all conflicts - then on the very next turn have an AI that was at war with me previous to the ceasefire attacked me. So what's the purpose of the ceasefire then - nothing. Either something is wrong here or they need to last x number of turns - as they are now, they are meaningless.

Grifman