beadm destroy error

Today when I was trying to destroy old boot environment, I got strange error:

# beadm destroy oi-hipster-2013-08-06
Are you sure you want to destroy oi-hipster-2013-08-06?
This action cannot be undone (y/[n]): y
be_destroy_callback: failed to destroy data/zones/build/ROOT/zbe: dataset is busy
be_destroy: failed to destroy BE data/zones/build/ROOT/zbe
be_destroy_zone_root_callback: failed to destroy zone root data/zones/build/ROOT/zbe
be_destroy_zone_roots: failed to destroy zone roots under zonepath dataset data/zones/build: dataset is busy
be_destroy_zones: failed to find and destroy zone roots for zone build
be_destroy: failed to destroy one or more zones for BE oi-hipster-2013-08-06

I didn't want to destroy zone root FS accidentally, so was a bit scared. However, after looking at it a bit longer, I found out, that zone root FS has several manual ZFS snapshots. After destroying snapshots I was able to destroy BE.