I would assume that its a bug.Ive never seen it happen by more then 1 vote though... maybe cause the "winner" was ranked higher, he got an extra secret vote, then cpu gave him the tie??
Honest and truly, I AM Robin Hood!
It happens to me some times too, I wonder if there is a hidden stat regarding how much the Papal States likes your faction or even if you are allied
Have seen this at least once or twice. Have also never won a tied vote.