As soon as I read your explanation, I felt my Japanese teacher reach across the years, slap me across the back of the head, and scold me for mixing kun-yomi and on-yomi in reading a single word.
Very helpful explanation.
Well, it's not common, but it does happen. Indeed, "kamiza" for 上座 is a mix of kun-yomi (kami) and on-yomi (za). I think the confusion arises from similar looking things (tokonoma and kamidana) and similar looking words (kamiza and kamidana). If you're operating in the language a lot, it's easy to remember the distinctions because of other associations. But if you're only speak dojo Japanese, it can be confusing. And even if you learn the language, if you don't use it, you lose it...fast!
I'm certainly not beyond making mistakes, either!