When you say "Caps Lock" are you referring to the ALPHA key? I don't recall there being a Caps Lock on that machine.
Of course, it's entirely possible that writing to the ROM was decoded separately and used for some control signals. The Apple ][ I believe did some interesting address decoding to get control signals from the address bus.
Looking at the memory map for the MZ-700 it appears that it implemented bank switching so that the ROM could be paged in or out and replaced with the video RAM and I/O ports. Some of those I/O ports are connected to the keyboard.
Of course, it's entirely possible that writing to the ROM was decoded separately and used for some control signals. The Apple ][ I believe did some interesting address decoding to get control signals from the address bus.
Looking at the memory map for the MZ-700 it appears that it implemented bank switching so that the ROM could be paged in or out and replaced with the video RAM and I/O ports. Some of those I/O ports are connected to the keyboard.
http://www.sharpmz.org/mz-700/coremain.htm#banksw