1) What happened
Input.inputString works differently on Windows and on Mac. Tested on Windows 8.0 and on OS X 10.8.5. When using Windows, inputString only works if the User presses two keys down almost simultaneously. If the user presses a single key, inputString will not have anything in it. This forces the user to write code checking if each key is down (Input.GetKeyDown) rather than just reading from the string. On OS X however this is not the case. inputString will populate with only a single key press and will populate with multiple key presses as well.

One would think that the inputString list would function the same no matter which OS the game was run on.

2) How can we reproduce it using the example you attached
Steps to reproduce:
1. Open the provided project.
2. If InputStringBug script is not already attached to camera, Attach it to the camera.
3. Press play and run the game.
4. Press and key down and notice the console window prints a statement depending on whether or not the key was read from Input.inputString or Input.GetKeyDown.
5. If using Windows press two keys simultaneously to get the inputString message to appear in the console window. (Holding down the keys does not work, both keys must be pressed at the same instant)
6. If using OS X you will notice that the message displayed is the inputString Message. If using windows you will notice that the GetKeyDown message is displayed.