If you are listening to a song and in the meantime scroll the list of artists in the left bar, but any list, by mistake, you press twice starts the first song found in the main window.
It also happens in the playlist list. You're listening to a playlist and while you're watching others you accidentally double-click and another one starts.
This leads to the interruption of listening to an album, playlist or whatever you are listening to.
In my opinion the start of a song should only be in the main window, where there is the song list.