Save for Web Doesn't Resize Image in Adobe Illustrator CS6

System:
OS X Mavericks (10.9.2)
Adobe Illustrator CS6 (16.0.4)

Symptom:
When exporting an AI file using the Save for Web dialog, after changing the resize percentage, the preview does not update to reflect the new Image Size, and the dimensions of the saved file is also incorrect. This seems to happen only when the image proportion is constrained, and only when changing the Percent box.

Solution:
Save for Web seems to save whatever you see in the preview box, so if the preview doesn’t resize, the saved file won’t be at the correct size either. The preview seems to be refreshed whenever the text cursor leaves the Width or Height box, or when the image proportion button is toggled. So if the preview doesn’t update after changing the value in the Percent box, you can either:

  • click the Width or Height box (or press [Shift]+[Tab]), and then click in another box (or press [Tab]), or
  • toggle the image proportion button (the one with the chain link icon near the Width and Height boxes).