as far as I am aware this is Android standard behaviour since Android 4.4.
One would need to root the device to get over that, granting the app superuser rights.
As long as I stick to '/storage/[SDCARD]/Android/data/com.orux.oruxmaps/files' all works for me, while I am only using that external SD card for map files and route/track files.
The path is different for the donate version, this has a different name (com.orux.oruxmaps.Donate).
Andy