Time Machine disabled in High Sierra b2 update 1

From the release notes to macOS High Sierra beta 2 update 1:


"New Issues


Time Machine is disabled for macOS High Sierra 10.13 beta 2 update 1 (17A291m). Apple recommends turning off Time Machine for APFS volumes on earlier versions of macOS 10.13 beta 2 as the space for snapshot files may not be freed correctly. (33006905)"


What does this mean? Is it not safe to back up using Time Machine starting with 10.13b2 Update 1?


Replies

As it plainly states, it is absolutely impossible to back up a beta 2 update 1 root volume, and previous beta 2 advised disabling Time Machine.


You didn't install this to your primary machine and upgrade your primary stable OS installation, did you?