The problem is you disabled fn_key_scancode in your remote.config. So the function key is 0x00 to switch remote mode and when you push Back on your remote the controller receive 0x00 and switch the mode. So find any free number like maybe 0x12 and change this in your remote.config:
before:
#fn_key_scancode = 0x4c
after edit:
fn_key_scancode = 0x12
Then it should work with this button (0x00) as fn_key_scancode is not anymore 0x00.