Personally, I think "mood disorder" is completely the wrong way of describe bipolar or the "mood" side of schizoaffetive. I say this because I have bipolar and this is what I think:

Depression, yeah, I get that. I lived with it a long time. Mania, sure, I get that too. But both of those are functional disorders that in turn supress my mood. If I'm just feeling sad/blue or whatever, that's not a big deal. If I'm totally devoid of motivation and my ability to make decisions, that's a huge problem. It's not because I'm sad. I can do things when I'm sad. I can do things when I'm happy. I can't do things when I cant concentrate or have 0 motivation. Those are not "moods" those are functional issues.

Likewise, in mania, racing thoughts are not a mood. They may frustrate and irritate me, but they are not a mood. Being over-productive is not a mood. Making big plans and grandios thinking are not moods. Those might cause me to become excited and giddy, but that is an effect of the functional problem that's happening.

Do you see what I'm saying? I feel like I"m rambling.

Anyway, I think the "mood" is a direct result of the functioning issue occuring, not the other way around.