Not sure I see this as a bug. If you look at your games application path I would assume the file extension is ZIP not 7z, and so LaunchBox doesn't see the item in the folder and marks it as removed. I will say unless MAME has changed recently or a RetroArch core is around that supports it 7z isn't a supported file extension for that emulator and you could very easily run into problems having your games in a 7z archive instead of zip.