You're bang on when you say diagnosing these things can be a bitch. Especially so with schizo-affective disorder where symptoms that are akin to schizophrenia and symptoms that are akin to bipolar are both present. I misdiagnosing twice has happened before landing on schizo-affective.

I had a relative who had this happen. Their symptoms seemed so much like schizophrenia, with bizarre delusions and voices. On the other hand, bouts of depression and bouts of hypomania were common. Before the mood component was fully realised, he was slapped with a Paranoid Schizophrenia diagnosis - which can particularly life shattering. A year or so later, a diagnosis of Bipolar was slapped on him, which is a bit of improvement because I believe the prognosis for Bipolar is markedly better than Schizophrenia.

Eventually, it was realised Schizo-affective Disorder fit the bill. After a bit of research, it turns out that such a diagnosis fit particularly well. The particular type of delusions commonly experienced by those with Schizo-affective disorder were present in him, amongst other things.

You can probably tell from what I've said above that it is indeed a bitch. It's almost life destroying and he was reduced to a lab rat in the process (finding the right medication is really a case of an educated guess and experimentation). I really am all for this sort of research because the more we advance with it, the less people will have to go through what my relative went through (and relatively speaking, he got off lightly).