-Done some testing about mentioned bug. Here is what I've found with a fresh and naked MameUI 0.226:
1-Launch one rom (outrun) and play. A outrun.ini is generated at the ini folder.
2-Create an arcade.ini with the following:
# CORE CONFIGURATION OPTIONS
3-Launch outrun again. The outrun.ini file is not created anymore. This should be the desired behaviour.
4-All The File, Play ... options from the WinGui at the top left generates again an outrun.ini in the ini folder, even with the arcade.ini with writeconfig 0 (Right click on the game, Play and Record input..., makes the outrun.ini appears again too)
5-If you run the command from cmd --> Mameui64.exe outrun -aviwrite outrun.avi, the outrun.ini is not created.
So it seems somehow those options from the GUI ignore the writeconfig 0 at arcade.ini