I see retropie is not using libretro core for dosbox, so I think it is an experimental or work-in-progress core.
I don't know how it works but you can google "dosbox lakka" or "dosbox retroarch" and see if you can find any help... Sorry...
Thanks for the input, although I am not using RetroPie (never used), I will do a search on google again to see if I can find something. Is there any alternative to play DOS games with my Pi3? I wanted to keep everything tidy and organized with Kodi and my video/movies library.