Cannot boot from BTRFS subvolume

**Describe the bug**

I tried installing RC3 with BTRFS on SSD disk, but it failed to boot. The boot loader could not find files under `/boot/` folder.

**To Reproduce**

1. Run the installer and create custom partition
* A 512 MB FAT32 partition at the beginning of the disk
* Remaining disk as a BTRFS partition
2. Follow the remaining installation steps, but shut down before it restarts to create the first user
3. Boot again with the installation media and use it in demo mode
4. Mount BTRFS partition somewhere in the demo session
5. Create subvolumes `@`, `@home`, and `@swap`
6. Move all the files into `@` subvolume
7. Create a swapfile under `@swap` subvolume and set necessary flags so that BTRFS can treat it as a swap file
8. Modify the `/etc/fstab` from the `@` subvolume so that `/boot/efi` is mounted to the FAT32 drive and `/`, `/home`, and `/swap` are mounted to their respective BTRFS subvolumes (with suitable options)
9. Create `/swap` folder under the `@` subvolume as a mount point for the swapfile under `@swap` subvolume
10. Run `update-initramfs`
11. Reboot the machine to complete the first user creation (this is where system fails to go any further from the boot screen)

Am I doing anything wrong? What am I missing? Do I need to manually reinstall GRUB or something?