I play as the Byzantine Empire, my ruler was ousted from the throne and I eventually played as his son, who was degraded to a Duke. Then a couple years later, somebody started a war on our new liege for my claim on the throne, yet I was actually the enemy of the vassal who started the war for my claim and sided automatically with the current liege. How does such a scenario even make sense? And why can't I switch sides during the actual war?