Both halves are rotating correctly around the Y axis, in opposite directions. The trouble is, without perspective, they do not look like they are rotating differently.
Applying perspective in this case basically makes one side of the image larger than the other side, as it rotates around the Y-axis. If there is no perspective, both sides of the image remain the same size, regardless of the direction the image is spinning.
Have a look at the whole image rotating without perspective, and imagine it is rotating in one direction. Then close your eyes, and when you open them again, imagine it is rotating in the other direction. Magic!