What i said, ignores mouse button flip.

so i use the windows setting to change left and right mouse button. Games that use window's setting will usually accept this (like the GOTY). The ingame menu will still say left and right button, when things for me are now Right and left button, and everything is fine.

in DX Revision however, left button is always left button, and right button alway right button even though on the desktop it is changed. I could go into the game's menu und change the button assignments for the two mouse buttons, but that still doesn't flip which button registers for menu presses.

it may sound confusing, but here's what you can do to test:
in the windows mouse settings, check the box to switch primary and secondary key.
run DX GOTY, see how all button actions including menu control are automatically flipped, without any manual assignments needed.
Now run Revision, see how not a single mouse button action is flipped and it's all back to right handed assignment. change mouse assignments in Revision's Keyboard and Mouse menu. See how now most things work except anything related to menus, which still remains on the right hand users index finger side.