I've discovered the way to fix $subj problem and is quite simple:
echo 0 > /sys/module/hid_apple/parameters/fnmode
This Chinese device pose as an Apple item (vendor ID 0x5ac), hence the usage of hid_apple driver:
Nov 06 09:18:36 rpi kernel: apple 0005:05AC:022C.0012: unknown main item tag 0x0
Nov 06 09:18:36 rpi kernel: input: Bluetooth 3.0 Macro Keyboard as /devices/platform/soc/3f201000.serial/tty/ttyAMA0/hci0/hci0:11/0005:05AC:022C.0012/input/input19
Nov 06 09:18:36 rpi kernel: apple 0005:05AC:022C.0012: input,hidraw0: BLUETOOTH HID v1.1b Keyboard [Bluetooth 3.0 Macro Keyboard] on b8:27:eb:4f:ff:99
Nov 06 09:18:36 rpi systemd-logind[11943]: Watching system buttons on /dev/input/event0 (Bluetooth 3.0 Macro Keyboard)
