can you go into some detail on just how you installed fedora 18 on the windows8 box
did you replace the windows MBR ( and the windows "recovery" partition ) with grub?
Did you put grub on the first linux partition
the hidden ( to windows) OEM's "recovery partition" often makes life difficult
in the grub menu.lis IS the windows8 section really pointing to windows 8 or is it pointing to the win8 "recovery" partition .
Also can you post the output of this from fedora