Ubuntu GNU/Linux Mate 16.04 LTS
Bottom line of a scaled image (a movie clip in my case) is stretched and repeated right to the bottom of the viewport. (Excuse my English, I'm not up on the blender nomenclature).
Attached .blend contains everything but the movie assets (because I don't know how to include them) but seems to only affect the scaling node. I've confirmed this works in 2.76b (released via Ubuntu) and doesn't work in 2.77a which I d/led from the official website.
This also seems to affect the translate node when the bottom of the incoming clip is raised above the bottom of the window. )