ATTENTION!!!
Here the solution at the problem of the two devices!!!
If we copy the file rkusb.tag into the root, restart and connect it to PC, we can see 2 devices,
but if you delete the file rkusb.tag, at the next restart the second devices (the hidden partition of the system files) doesn't disappear!...
This happens because we must replace some system file before deleting rkusb.tag!!!
Go to /Resource/BID of the hidden partition
I tried to copy BMP0.BIN on my PC, then I've deleted BMP0.BIN in the folder, then I've modified BMP0.BIN (changing some images with RK27UIEditor2) and recopied this BMP0.BIN from the PC to the folder of the hidden partition.
Then I've deleted the file rkusb.tag, disconnected the MP5, so a red screen appears, because it's changed some images, and finally I've restarted the MP5 ...
So with the next connections the hidden partition disappear!!!