Comment # 17 on bug 1142229 from Neil Rickert

>Neil - another issue can be that some BIOSes refuses to boot from disk if there is no primary partition with active flag.

I don't doubt that, though I have never had such a system.

In that case -- MBR gap too small, "btrfs" in a logical partition, BIOS needs
primary active flag -- it might be impossible to boot.  Well, actually, it
could be booted using "altmbr.bin" from "syslinux" because that ignores the
active flag and can be configured to boot a logical partition.  But I don't
think the installer should ever try that.