It's not different, because the left-right flip by the lens is part of a rotationally symmetric image translation (that also flips up for down, e.g.), not a bilaterally symmetric reflection. With the rotation, there is no change in the relationship of parts of the image one to another, relative to our personal orientation, the way there is in the reflection, so it's trivial for the brain to account for it - up on the retina is always down in the real world, left on the retina is always right in the real world, etc.