I have Arch 7.1 working fine on this box in a small partition on drive /dev/hda and I though I would do an install of 7.2 on a large partition on /dev/hdb replacing another distro. I have now installed three times to two different partitions and can report that grub is acting very odd.
You may boot into Arch 7.2 after the install one (1) time. Do as much or little as you like because that is the only boot you are going to get. The next time you select Arch it will give an error complaining about being unable to read this or that.
Mind you, the main boot-loader is grub and it is calling on a grub installed in /dev/hdb2 which worked the one time. The 7.1 install is fully updated and it still works great, I just can not install Arch 7.2.
Well, I got the job done. I downloaded a copy of Arch 7.1 and installed that. I used pacman to bring it up to 7.2 (I think it went well) and grub acts normally.
I have no clue why I have trouble here with 7.2 and no one else reports trouble --- bad karma I guess.