sync doubles music on iphone

Hello

Here's a strange one:

After updating to the previous version of iTunes (the one which underwent the first major redesign), and my iphone to IOS 7, there's lots of inconveniencies occurring.

The funniest one is this:

When I connect the phone and sync it with itunes, it says something like

"17,25 gb / 2230 tracks of music"

then I make some minor changes (add or remove a playlist/album for example) and the usage drops to

"9,38 gb / 1395 tracks of music"

the sync goes on, most of the time flawlessly, and as soon as it is finished, the file-count jumps back up to the higher number...

See the screenshots for a better insight...

Any ideas what could cause it?