Bootloader doesn't install after 12.04 > 13.04 on macbook

I have had Ubuntu 12.04.2 installed on my 2009 macbookpro, ran great, installed without problems. Burned a new dvd with 13.04 the other day and was going to install from scratch. Hit "try ubuntu" and install, then spotted the "upgrade 12.04.2 to 13.04" option and chose that. Everything seemed fine, until the "cannot install bootloader" box appeared. Tried to install to sda and sda2, but it didn't work. Install finished successfully anyway though.

After install completed, while still logged into the live dvd, I ran:

ubuntu@ubuntu:~$ sudo mount /dev/sda2 /mnt
ubuntu@ubuntu:~$ sudo grub-install --root-directory=/mnt /dev/sda
/usr/sbin/grub-bios-setup: warning: Sector 32 is already in use by the program 'FlexNet'; avoiding it. This software may cause boot or other problem in future. Please ask its authors not to store data in the boot track.
Installation Finished. No error Reported.
ubuntu@ubuntu:~$

Boots fine after that.
Sry for crappy bugreport, I don't really know what to write :/

ProblemType: Bug
DistroRelease: Ubuntu 13.04
Package: ubiquity 2.14.6
ProcVersionSignature: Ubuntu 3.8.0-19.29-generic 3.8.8
Uname: Linux 3.8.0-19-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.9.2-0ubuntu8
Architecture: amd64
CasperVersion: 1.331
Date: Sun Jun 23 06:22:16 2013
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz.efi file=/cdrom/preseed/ubuntu.seed boot=casper quiet splash --
LiveMediaBuild: Ubuntu 13.04 "Raring Ringtail" - Release amd64 (20130424)
MarkForUpload: True
ProcEnviron:
 TERM=unknown
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)