In this thread someone posts about a fix for the Twenty Twelve IE 8 Menu issue:
My question is, should I apply this fix myself, or wait for to be applied to the Twenty Twelve theme? (Also, will it be applied?)
The fix involves making changes to the Functions.php file. I use a child theme and am not sure I should be making changes to the parent theme functions file - won't it be overwritten if the theme gets updated?