> For Mother, there isn't any mid-frame Chr-Bankswitching while the menu is open, so this is not the actual problem.

Oh yes there is. It's switching CHR banks twice every SCANLINE at each location that contains English text (since it doesn't have enough room to display both A-Z *and* kana at the same time).

--
Quietust
P.S. If you don't get this note, let me know and I'll write you another.