Even if they're all on elective they require separate votes. Each kingdom/empire title can have different succession laws which can really mess things up. Or maybe you have more than one kingdom/empire title - If that's the case, try to stick to only 1 kingdom/empire title when you have elective. I'm pretty sure that trait should be cut out of succession entirely with elective succession, but maybe not. It can do funny things to succession, but if it is somehow the case that the younger one doesn't have it, granting the 'Despot' title to him will also count as having the trait for succession purposes. One is it might be something to do with the 'born in the purple' trait, but that doesn't make much sense since if the older sibling has it, the younger one definately should. Neither of which sounds right TBH, but it might give you an idea of where to look.
