files_download_zip_to_file creates a zip with upper and lower duplicates folders

when I use dbx.files_download_zip_to_file(...) if the folder to zip is in uppercase,e.g.
ML with files and folders inside: file1 RL
the zip contains duplicates folders (in apper and lower case) e.g. ml and ML, and RL and rl, some of such folders are empty other with the expected files.