I have a script where user can set specific folder path to work with. So I have a string property in property group class:

cls.conf_path = bpy.props.StringProperty(name = "Path to textures", default = "",  description = "Sets the path to texture folder", subtype = "DIR_PATH", update=updateString)

In panel I have just this:

MaterialProps = bpy.context.active_object.active_material.props
row = layout.row()
row.prop(MaterialProps, "conf_path")

The problem:

I tried a lot of folders on my PC and everything works fine (Win10), but when my friend tried to use my script on his PC (Win10 too) when he chose path something like C:\Users\USER\some_folder, string property becomes //..\Users\USER\some_folder\ and obviously script cant find such folder. In my case I tried to work with folders on C disk on my PC and its ok. What it could be?