Originally Posted by otichy
Maybe the freedownloader should run from somewhere else than /mnt/us ?
Yes, it shouldn't open any files on the user store (including its own executable) and this is quite tricky because downloading file usually means opening a file in the user store for writing. Any open files would prevent unmounting the user store on Kindle side when the USB cable is connected to host.
Another option is to stop the service whenever the USB connection is detected - I suppose usbnetwork's ssh daemon is working like that.