JSON blocking/timeout with Player.Open

When starting a playlist of images using Player.Open thru a JSON request, I get no reply until the player is stopped.
Is this correct behaviour ?

This is rather annoying as it causes plugin code to completely hang.
First observed using the python api, I confirmed with curl as well.
I’m running Kodi 17.0 under Ubuntu Linux.

The request which hangs is:
{“jsonrpc”:”2.0″,”method”:”Player.Open”,”params”:{“item”:{“playlistid”:2}},”id”:1}

Thank you for your help.