"request MappingKeyboard" not generated for FN+KP_ENTER

[Stefano Facchini]

I'm trying to configure the key FN+KP_ENTER (hotkey ATKD 0000005b) to
start a calculator. Since this key wasn't recognized, I added an ACPI
event and used acpi_fakekey as follow:

/etc/acpi/events/calc:
  event=hotkey ATKD 000000b5
  action=/etc/acpi/calc.sh

/etc/acpi/calc.sh:
  #!/bin/sh
  . /usr/share/acpi-support/key-constants
  acpi_fakekey $KEYCALC

After this, I can get an XF86Calculator event hitting FN+KP_ENTER, but
only after pressing another (any) key. With xev I discovered that all
the FN+something keys generate a "request MappingKeyboard" event before
generating the "keypressed" event. Are these behaviours related? How can
I fix this?

Thank you