This is the current issue.
I have a project where I am simply increasing the scale using the transform effect. In order to get motion blur, I have unchecked use composition shutter angle and increased the shutter angle to 200. When changing the scale, the image will now have the motion blur but the shape is moved away from its original position (not in the center anymore) when GPU Acceleration renderer is selected.
This is what it looks like when GPU Acceleration renderer is selected
This is what it looks like when Mercury Playback Engine Software is selected
This bug is pretty annoying. As rendering with Software Renderer is extremely slow. Please let me know what can be done and if you are working on this.