Still a GPG issue, or is it me?
$ wget -qO - 'https://bintray.com/user/downloadSubjectPublicKey?username=openhab' | sudo apt-key add -
OK
$ sudo apt-get update
Hit http://archive.raspberrypi.org jessie InRelease
Hit http://mirrordirector.raspbian.org jessie InRelease
Ign http://dl.bintray.com stable InRelease
Get:1 http://dl.bintray.com stable Release.gpg [821 B]
Get:2 http://dl.bintray.com stable Release [3,695 B]
Hit http://archive.raspberrypi.org jessie/main armhf Packages
Ign http://dl.bintray.com stable Release
Hit http://archive.raspberrypi.org jessie/ui armhf Packages
Hit http://mirrordirector.raspbian.org jessie/main armhf Packages
Get:3 http://dl.bintray.com stable/main armhf Packages [20.5 kB]
Hit http://mirrordirector.raspbian.org jessie/contrib armhf Packages
Hit http://mirrordirector.raspbian.org jessie/non-free armhf Packages
Hit http://mirrordirector.raspbian.org jessie/rpi armhf Packages
Ign http://archive.raspberrypi.org jessie/main Translation-en_GB
Ign http://archive.raspberrypi.org jessie/main Translation-en
Ign http://dl.bintray.com stable/main Translation-en_GB
Ign http://archive.raspberrypi.org jessie/ui Translation-en_GB
Ign http://archive.raspberrypi.org jessie/ui Translation-en
Ign http://dl.bintray.com stable/main Translation-en
Ign http://mirrordirector.raspbian.org jessie/contrib Translation-en_GB
Ign http://mirrordirector.raspbian.org jessie/contrib Translation-en
Ign http://mirrordirector.raspbian.org jessie/main Translation-en_GB
Ign http://mirrordirector.raspbian.org jessie/main Translation-en
Ign http://mirrordirector.raspbian.org jessie/non-free Translation-en_GB
Ign http://mirrordirector.raspbian.org jessie/non-free Translation-en
Ign http://mirrordirector.raspbian.org jessie/rpi Translation-en_GB
Ign http://mirrordirector.raspbian.org jessie/rpi Translation-en
Fetched 25.0 kB in 15s (1,640 B/s)
Reading package lists... Done
W: GPG error: http://dl.bintray.com stable Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 379CE192D401AB61