OSX 10.11 El Capitan / Sierra and Kinesis Freestyle 2 Bluetooth little glitch

UPDATE 2017-04-25: this solution came in handy when I had another glitch with Sierra: keys would lag or repeat very erratically. Tried resetting pram etc to no avail, so then I performed these steps out of desperation and it all went back to normal.

After upgrading to El Capitan, my Kinesis Freestyle 2 Bluetooth keyboard had a small issue, which I'm documenting here in case other people hit it.

Basically, after installing the OS update, F*/special keys were dead. Solution:

1.  Open System Preferences -> Bluetooth
2. Click on the X icon to the right of the keyboard, in order to un-pair it.
3. turn the Kinesis off, then on again, and press the CONNECT button at the back of the keyboard
4. The keyboard should pop on the screen, select it and pair it again (you will have to type a few numbers shown on screen)

All done! You should now have your special keys back.