Comment # 11 on bug 1142229 from Neil Rickert

>well, for me it is more likely just coincidence that it is the first logical partition or qemu do some magic in its BIOS as on real hardware it is problem with jumping to boot code on logical partition. Does it work if logical partition is not the first one?

I doubt that there is any special magic.  And I doubt that it  matters which
logical partition is used.

My partition (in a VM) was about the same as described in comment 4 above. 
However, I carefully created the first partition so that there was minimal
space between the MBR and the first partition.  Normally, there would be 2047
blocks there.  I used:
parted -a cylinder /dev/sda

I then created a new label (msdos partitioning), and a new partition.  I set
the first partition to start at offset 0M.  And parted set the partition to
begin the first sector beyond the MBR.

Here's the real problem:

When I tell the installer to boot from a partition, it normally chooses the
partition containing "/boot".  But it makes an exception.  If the partition
containing "/boot" is a logical partition, then the installer changes that to
boot from the extended partition.  And if "/boot" is part of a "btrfs"
partition, that is never going to work.

I understand the reasoning for this behavior.  Traditionally, one can only boot
from a primary partition.  But the generic code that the installer puts in the
MBR can actually boot from a logical partition.  And, in case "/boot" is in a
"btrfs" partition, it should just go with installing booting there and setting
that logical partition as active.