[kbd] Plus instead acute accent

[DGSJ]

Hello:
I'm working in a customized Linux distro for Raspberry Pi 3 B+, in 64-bit
architecture, with a Raspbrerry kernel, version 5.6.4-v8+.

I'm using to control the terminal kbd-2.2.0, cross-compiled from source, 
and Graft as package manager.

I'm having a problem with Spanish acute accents in vowels. If you try to
write an acute accented vowel, for example á, this is what yo see in the
screen:

$> +a

It is to say, the dead key is not working, and moreover, instead of the
acute accent, the plus symbol is displayed.

There are other symptoms of the misconfiguration:
key    ´¨{    displays    +*~
key    `^[    displays    '(circumflex s)º
key    +*     displays    [{
key    }ç     displays    ]}

Fortunately ñ and Ñ work fine ;-), and the rest of the keys are ok.

Here are some details about the console and the keyboard.

- Console.
It is an interactive login shell invoked after boot with agetty, I mean
it is not a GUI console. The framebuffer supports graphics. 

Regarding the environmental and console variables:
LANG=es_ES.ISO-8859-15 at euro
TERM=Linux
FONT=lat0-16

- Keyboard
According to 'kbd_mode' the keyboard is set in Unicode mode (UTF-8), the map
is es ('loadkeys es').

Well, I think I've missed something to make the accents or the deadkeys work.

Any help will be welcomed. Thank you in advance for your cooperation.

-------------------------
Daniel Gutiérrez