Solved ZFS which directories ignored in rollback?

I am have trouble understanding what is included in zfs recursive snapshots and rollbacks.

zroot  1.93G  206G  128K  /zroot
zroot/ROOT  482M  206G  128K  none
zroot/ROOT/default  482M  206G  482M  /
zroot/tmp  128K  206G  128K  /tmp
zroot/usr  1.46G  206G  128K  /usr
zroot/usr/home  6.48M  206G  6.38M  /usr/home
zroot/usr/ports  828M  206G  828M  /usr/ports
zroot/usr/src  662M  206G  662M  /usr/src
zroot/var  1.12M  206G  128K  /var
zroot/var/audit  128K  206G  128K  /var/audit
zroot/var/crash  128K  206G  128K  /var/crash
zroot/var/log  410K  206G  298K  /var/log
zroot/var/mail  213K  206G  128K  /var/mail
zroot/var/tmp  128K  206G  128K  /var/tmp
zfs snapshot -r zroot/ROOT/default@FreshInstall.10.2-r

If I put a test file in 6 locations, 3 disappear with the rollback, 3 do not. I cannot seem to find what the "rules" are in the handbook.

For example, /var/testfile goes away, /var/mail/testfile does not. This would make sense, but I am not sure how to determine what directories are included.
Also note, even if it did work recursively, there are no datasets 'below' zroot/ROOT/default so only this filesystem would be affected. For zroot/var things would be different as the recursion would also involve zroot/var/audit, zroot/var/crash, zroot/var/log, zroot/var/mail and zroot/var/tmp.

It doesn't matter where the filesytem is mounted in the end, the recursion is seen from ZFS's point of view, not the filesystem's.