System Information
Windows 7 Professional Service Pack 1
NVIDIA GeForce GTX 660

Blender Version
Broken: 2.75a c27589e

Short description of error
Using the map uv node in the compositor produces image artifacts. The uploaded images show one example image input, an example uv map and the result. The uv map is smooth and has no jumps, but the edges of the square in the output image look jagged. Also note that the output should not show the white line around the circle because there actually is a sudden change to black in the uv map. My guess is that there could be something wrong with the image coordinates used to access the uv map and/or the pixel weights used for filtering when applying the uv map.

Exact steps for others to reproduce the error
Attached is a simple blend file that renders a white square in low resolution and some linear texture coordinates that should not change the image when used as a uv map (though they change it a little). The composite node also adds a small offset to the uv map over time. So when stepping forward frame by frame the white square will slowly move; However, every two pixels it moves, it seems to jump back one pixel.