I agreed to a declaration of friendship (DoF) with one civ, but she attacked me about 10 turns later. I eventually signed a peace with her and she was immediately friendly to me. No grudge. Because she attacked me, I assumed that the friendship was over. When I open a dialog with her, I can ask her to make a joint DoF. But apparently, I still have a DoF with her? When I tried to attack her about 30 turns later, I got labeled a backstabber and got negative diplomacy with every civ. This doesn't make sense.