This is just to thank deloptes, solitone, Leandro for their suggestions. Unluckily, none of them helped solve the problem. I'm waiting for 'stretch' to be officially the new 'stable' debian version on 5th February so as to fully upgrade my system (now it is partially Jessie, partially Stretch) and check again whether or not bluetooth works with this quite old keyboard.
At present I only get a large variety of errors, depending on the commands used to attempt pairing and may be I'm missing something: The link suggested by Deolptes brought me to a 'pin-code-database.xml' file that should be in gnome-bluetooth directory, not present in my system (broken dependencies). Yes, I have the latest 'bluez-firmware' version. AAMOF, prior to installing stretch bluetooth applications to the base Jessie version, I got the same errors when I tried bluetooth in Jessie. What upsets me most is that the keyboard worked nicely under Squeeze/bluetooth running on a debian ppc on a macmini older than the one I'm using with Jessie (intel amd64). Thanks again to you all. Regards, Ennio -- [Perche' usare Win$ozz (dico io) se ..."anche uno sciocco sa farlo. \\?// Fa' qualche cosa di cui non sei capace!" (diceva Henry Miller) ] (°|°) [Why use Win$ozz (I say) if ... "even a fool can do that. )=( Do something you aren't good at!" (as Henry Miller used to say) ]