ZFS allows deletion of files in a sticky directory

I have found that directory entry may be deleted from a ZFS directory
with the sticky bit, if "the entry is a plain file and you have write
access"
(this is citation from a comments in zfs_dir.c)
But this behavior isn't described in the sticky(8) and isn't allowed on a
UFS.
The attached patch provides the UFS-like behavior of a sticky directories on
a ZFS.
Is this bug or feature?

-- 
Alexander Zagrebin