The mtp kioslave can be used to access mobile file system. I can copy a folder structure with sub folders to the device if not existing. If a sub folder exist already, an error message box is shown up "Can't create folder" and the copy task is aborted. It would be better to skip folder creation in this case and just try to write the content into the existing folder on the device.
Can reproduce on git master too.
Still existing on frameworks 6.13.0 :(