ZFS objects used to store extended attributes are not deleted when parent file/directory is deleted. Those objects still occupy disk space but are otherwise unreferenced and can't be deleted.

So far I've traced it down to sys\cddl\contrib\opensolaris\uts\common\fs\zfs\zfs_dir.c:zfs_rmnode.
ZTOV(zp) is NULL for extended attributes directory (object 9) so zfs_purgedir is not called and object 10 is left alone.

How-To-Repeat: # zfs create -o mountpoint=/test root/test
# touch /test/file1
# setextattr user test abc /test/file1
# zdb root/test
    Object  lvl   iblk   dblk  dsize  lsize   %full  type
         8    1    16K    512      0    512    0.00  ZFS plain file
         9    1    16K    512     1K    512  100.00  ZFS directory
        10    1    16K    512    512    512  100.00  ZFS plain file

object 8 - the file,
object 9 - extended attributes directory,
object 10 - value of the 'test' extended attribute ("abc")

# rm /test/file1
# zdb root/test

    Object  lvl   iblk   dblk  dsize  lsize   %full  type
        10    1    16K    512    512    512  100.00  ZFS plain file

objects 8 and 9 are deleted, object 10 is still there (leaked).