Often, this happens:

. I execute synching for my removable media
. At the end of the synching I notice that one or more playlists lack some songs.
. I investigate and I found that the file that lacks is the file XXX
. Anyway if I check the removable media's filesystem, I find the file XXX
. I eject the removable media
. I insert again
. I execute another synching
. RB asks me if I want to replace the file YYY because the file YYY already exists on the removable media.
. Independently form my selection, at the end of the synching  the file YYY is showed neither in any playlist nor in the root of the media player.
. Anyway if I check the  removable media's filesystem, I find the file YYY

. The files XXX and YYY maybe or not maybe the same file.

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I've investigated a bit the source code hoping to find a solution.

During the first synching I think that the problem is that:
. As the batch transfer is finished, the function 
[ g_idle_add ((GSourceFunc) sync_idle_cb_playlists, source);] rb-media-player-source.c : 587
is called immediatly, before that the event  RHYTHMDB_EVENT_METADATA_LOAD is received for the last songs, so this songs, when sync_idle_cb_playlists() is executed is not yet inserted in the removable media player source model. In fact this happen only after receiveing the event RHYTHMDB_EVENT_METADATA_LOAD ( at least I think... )