I assume this has to do with the fact that the cellar is attached to a ground level shack above it but a stairwell lower, apparently without leaving the cell. I don't know if this error exists in other attached cellars (the Legion safehouse, Beer Distilling Shack, ect.) because the character that visited those locations, has been deleted, and I haven't discovered them with my current character.
This bug would seem minor, and probably is in the scheme of things, but i'm constantly using many of these overlooked areas as "home bases" ect, and it eliminates the location's usefulness if I can't safely drop items.