stretch/KDE: bluetooth: unable to connect

[solitone <solitone@mail.com>]

Hi all,

can't get the bluetooth work in scratch. From KDE Bluetooth Device Wizard, I 
see the device I want to pair with (e.g. an android tablet), I select it, I 
confirm both on debian and on the tablet that the pairing code I see is 
correct, but then the Bluetooth Device Wizard says that the setup of the 
tablet has failed.

Here's what I find in /var/log/messages:

Jan 18 21:35:59 alan NetworkManager[585]: <info>  [1484771759.2687] keyfile: 
add connection in-memory (545449fa-f0ae-4027-8a3f-ee9444beb0b2,"Nexus 7 
Network")
Jan 18 21:35:59 alan NetworkManager[585]: <info>  [1484771759.2704] bluez: BT 
device Nexus 7 (AC:9E:17:C7:F1:43) added (NAP)
Jan 18 21:35:59 alan NetworkManager[585]: <info>  [1484771759.2713] manager: 
(AC:9E:17:C7:F1:43): new Bluetooth device (/org/freedesktop/NetworkManager/
Devices/24)
Jan 18 21:35:59 alan NetworkManager[585]: <info>  [1484771759.2716] device 
(AC:9E:17:C7:F1:43): state change: unmanaged -> unavailable (reason 'managed') 
[10 20 2]
Jan 18 21:35:59 alan NetworkManager[585]: <info>  [1484771759.2835] device 
(AC:9E:17:C7:F1:43): state change: unavailable -> disconnected (reason 'none') 
[20 30 0]

It is that disconnection for no reason that is suspicious to me. Any idea?

Cheers,
  Davide