Jon, There is a check box for "Ignore mixed case".

Checking it never seemed to "stick" as Bert says above. I just checked it again and will see how long it lasts.
I tried this and it did not stick at all. Ben, or anyone else... open a note, hit F7 to spell check, and hit options. Click on "ignore mixed case". Finish spellchecking, close the chart and go to a different one. Re-open options and it isn't checked. So I guess you could check it for each and every note, but that kind of defeats the purpose, doesn't it?