OL7 Alternate Snapshots as the root File System

With pretty much confidence on the subject of alternate boot environments on OL6 using BTRFS root fs, I tried the same steps on OL7.2 (using the UEKR4 kernel if that matters). To my disappointment, when I completed the OL7 installation, I noticed that there was not "install" snapshot and and switching between boot environments (ie different snapshots of root subvol) didn't work. Initially I thought that the process has changed in OL7, but then I saw in the Administration Guide of OL7 (E54669, 21.13 About the Btrfs root File System) that nothing should have changed.

Anyway the point is that OL7 fresh install never leads to a filesystem layout such as the one pointed by the aforementioned doc and more importantly the "btrfs subvolume set-default <id> /" fails to change the default root snapshot on the next reboot (you have to alter manually the kernel boot args in grub).