Updated from 17.4 to 17.4.2 on Gentoo Linux.
Previously, using 17.4 I could drag&drop YouTube video links to the smplayer window, and it would automatically play them. Now on 17.4.2, it doesn't. When I drag&drop a link, it does get put in the playlist, but doesn't start playing.
Note: I drag&drop it inside the main area of the smplayer window, NOT inside the playlist window.