zfs command dumps core

Hi List,

# uname -a
FreeBSD antares.takwa.de 12.0-ALPHA6 FreeBSD 12.0-ALPHA6  r338827  amd64

here, if I issue

# zfs get all

I get

Assertion failed: (avl_find() succeeded inside avl_add()), file /usr/src/sys/cddl/contrib/opensolaris/common/avl/avl.c, line 649.
Abort (core dumped)


Thanks,
   Michael