My issue is the same across 3 different Sega Genesis emulators I have tried Bizhawk, Kega Fusion and Genesis Plus GX in Retroarch. When I am using a mouse as a emulated Sega Menacer light gun, the start button on the regular pad controller does not work to continue. The basic control set up is P1 Port 1 is mapped to a joypad/controller with start button binded to physical start button on either a xbox 360 or PS4 wireless controller. P2 Port 2 side has a Mouse used as a emulated Menacer Light gun. So after starting the game with the Start button on the Port 1 joypad, and selecting the menu option to begin game using the Menacer in P1 side (T2: Arcade Game) for example. The Menacer works fine to control as far as shooting and tracking with crosshairs etc...however when I die and need to press start to use a credit and continue, the start button on the joypad no longer works. None of the other mouse buttons beside Button 0/1 and Button 2 do anything on the physical mouse. Pressing them does not work as a start button as well. I tried 2 games and both had the exact same issue, Body Count and T2: Arcade Game.