Not quite a bug, but I haven’t been able to figure out how to solve this issue when running arcade games under FBA (in this case, I was trying to load a Neo-Geo game):
RetroArch: [libretro INFO] :: WARNING! Button unaccounted for: [Reset].
RetroArch: [libretro INFO] :: Reset - has nSwitch.nCode: 3d.
RetroArch: [libretro INFO] :: WARNING! Button unaccounted for: [Test].
RetroArch: [libretro INFO] :: Test - has nSwitch.nCode: 3c.
RetroArch: [libretro INFO] :: WARNING! Button unaccounted for: [Service].
RetroArch: [libretro INFO] :: Service - has nSwitch.nCode: a.
RetroArch: [libretro INFO] :: WARNING! Button unaccounted for: [Dip 1].
RetroArch: [libretro INFO] :: Dip 1 - has nSwitch.nCode: 0.
RetroArch: [libretro INFO] :: WARNING! Button unaccounted for: [Dip 2].
RetroArch: [libretro INFO] :: Dip 2 - has nSwitch.nCode: 0.
RetroArch: [libretro INFO] :: WARNING! Button unaccounted for: [System].
RetroArch: [libretro INFO] :: System - has nSwitch.nCode: 80.
RetroArch: [libretro INFO] :: WARNING! Button unaccounted for: [Slots].
RetroArch: [libretro INFO] :: Slots - has nSwitch.nCode: 1.
RetroArch: [libretro INFO] :: WARNING! Button unaccounted for: [Debug Dip 1].
RetroArch: [libretro INFO] :: Debug Dip 1 - has nSwitch.nCode: 0.
RetroArch: [libretro INFO] :: WARNING! Button unaccounted for: [Debug Dip 2].
RetroArch: [libretro INFO] :: Debug Dip 2 - has nSwitch.nCode: 0.
Said mapping issues prevent me from adjusting DIP switches, entering service menus, and otherwise configuring the virtual arcade machine, but the features seem to be there, only inaccessible by default.