Why do seam edges move together? I have a cube where I am trying to move one UV edge that happens to be a seam. My understanding is that since the edge is marked as a seam, it should be separate from surrounding edges, but when I move the edge other vertices/edges move as well. Why does it do this? Specifically, since the edge is marked as a seem, shouldn't it be moving independently? 

Thanks,
Make sure you have the Edge Selection enabled (3 vertical line icon), as well as the individual vertex selected (3 white dots).