How do I sync music to my Android with Clementine?

I'm not sure why Clementine doesn't find songs at first, but I can transfer musics anyway:

Right click on a track and select "Copy to device...", it might take a while, but it works, at least it did for me (You'll see a progress indicator saying "Organising files..." under play controls).

Btw my device is Nexus 4 with Android KitKat and I'm using Clementine 1.2.3.

Clementine Sync