/root on a separate dataset breaks FreeBSD-base installation

[Grzegorz Junka]

I am following https://wiki.freebsd.org/PkgBase

This:

pkg install -g 'FreeBSD-*'

fails with this:

[2/800] Extracting FreeBSD-runtime-12.1_3:   4%
pkg: Fail to create hardlink: 
/root/.pkgtemp..cshrc.v5sxGCRu3GlP:Cross-device link
[2/800] Extracting FreeBSD-runtime-12.1_3: 100%

/root is in a different ZFS dataset. It works fine if it's not. Why pkg 
is using /root/.pkgtemp instead of /tmp or /var/tmp? It doesn't matter 
from where I run the command, looks like the path is hardcoded.

Can I workaround with some option to pkg?

GrzegorzJ