Its not that surprising considering that every image hitting our retina is reversed by our brain.
Processing visual information is a complex task,it takes up a relatively large portion of the brain compared to other senses. The optic part of your brain's job is to make images right-side-up. It does this because your brain is so USED to seeing things upside-down that it eventually adjusts to it.
With so much visual processing going on all the time, this is probably a walk in the park for our grey matter. :-)
