I tried it with cec-client, and it seems to be some sort of timing issue ?
Ubuntu Pastebin (cec-client log)
If the Pi CEC client is marked as active source, it is getting keys. Then at message 11850, the tv is turned off, then at 17327 it is turned back on. Then it is not getting key presses until i type "as" into cec-client, marking it as an active source again - and at that moment, i am getting the key presses again (message 39055 and later).
This is with LE 7.0.1, Samsung 55JU6400, firmware 1470.