Thank you Rene, I really appreciate you listening and responding so quickly smile

Good news is that your updated binary fixes the bug. The command MAME command line no longer has the unnecessary bits. For example:
11:49:52.412: starting emulator #3, command = E:\emu\MAME\mame64.exe -mouse -nojoystick -autoframeskip -multithreading -rompath "E:\emu\+Images\ROMS;E:\emu\+Images\Software_Lists" -hashpath "E:\emu\MAME\hash" -artpath "E:\emu\MAME\artwork" hp9845a
11:49:52.602: emulator #3 started, PID = 244939040, running emulators = 1
11:49:59.546: emulator #3 finished, exit code = 0 (no error), exit status = normal, remaining emulators = 0

There is just one low-priority oddiy remaining that you might be interested in. The bloom_overdrive Option always has the 'Reset to default value' button constantly highlighted, no matter that it's already at Default. I've not noticed this behaviour elsewhere in any other Options, so it's probably confined to this one case.

Thanks again for your efforts! It's been fun to play my part in this process. Hope it helped.