Just as an FYI, I just did a hexdump of both /dev/sda and /dev/sdb on a machine I originally installed as 4.2 (and without manually grubbing) and both drives look like the first sector has something boot related on them, with text like:
Loading PBR for descriptor 1....done....failed....Bad boot flag... active partitions...PBR load error...Bad PBR signature........
So I guess the installer got it right.
-Steve