It has been reported with some emulators. Mame I have seen reported a couple times. I do not think anything was resolved as it seems to be something not very many experience or are reporting. I justed tested Arcade64 and saw no issue. That being said I have not seen it with any Mame variant (standard Mame, MameUI, GroovyMame, or Arcade64).
Are you using the new Startup themes released in the latest LaunchBox stable build?