The mirror doesn't reverse the text.
Put your right hand up to the mirror. Which hand in the mirror moves? The right one. Move your hand up - and the image of your hand moves up as well. It doesn't reverse your right hand to be on the left hand side.
We require text to run from left to right. Hang the text in front of the mirror and go sit with your back against the mirror - looking toward the text. The text looks fine, because it runs left to right.
Then go back to your original position - the text is incorrect because it's running from right to left.
The issue is not that the mirror is doing something funny to the text. It's that you aren't facing the image of the text you're looking at.
Originally posted by joneschrah, and they told me there were no more wise men..:-)
To further illustrate the issue - mirrors CAN make the text appear up-side down. Take your book, and rather than turning it around on the horizontal axis toward the mirror, flip it upside down to face the mirror. Now, suddently, it's upside down but still correctly running left to right.