File>Export>Save for web> - When you change the size percentage, the new width and height number appear. The preview of the image does not change to reflect the new size. The resulting saved image does not reflect the new size. Only workaround is if you slowly click on width and height numbers, wait for the preview of the image to display the new size, and then click save. This has been a problem with all versions of Illustrator that I can remember. This happens on both Mac and PC, on all of the OS versions that I have been able to test on.