YouTube pushes playlists in the new layout.

There is a checkbox to include the playlist if the video you are watching is from one. By default it will start the playlist at "current video" but you can change it to "start of playlist".

Important point here, if you only want to sift the one video, make sure to untick that checkbox!

The easiest way avoid sifting a playlist using the "submit to videosift" bookmarklet is, probably..., to click on the "share" tab, untick the playlist option, copy the video URL, click "submit to videosift", and then paste the url into the embed box over the top of the one the bookmarklet picked up.

What I usually do though is right click on the video, get url, open the url in another tab, and then click the "submit to videosift" bookmarklet from there.