Deleted files in directory

I was just refreshing my knowledge about filesystems... In FreeBSD it is definately easier to investigate fs behavior. You can just do a hexdump of a directory. In Solaris and Linux this does not work. Hexdump of zfs directory is not very interesting. However, in ufs dump we can see that deleted files persist in directory listing:

# zfs create -V 1G zpool/zvol1
# newfs /dev/zvol/zpool/zvol1
# mkdir test
# mount  /dev/zvol/zpool/zvol1 `pwd`/test
# cd test
# mkdir 99
# cd 99
# touch a b c d e
# hd . 
00000000  00 14 01 00 0c 00 04 01  2e 00 00 00 02 00 00 00  |................|
00000010  0c 00 04 02 2e 2e 00 00  01 14 01 00 0c 00 08 01  |................|
00000020  61 00 05 9e 02 14 01 00  0c 00 08 01 62 00 05 9e  |a...........b...|
00000030  03 14 01 00 0c 00 08 01  63 00 05 9e 04 14 01 00  |........c.......|
00000040  0c 00 08 01 64 00 05 9e  05 14 01 00 b8 01 08 01  |....d...........|
00000050  65 00 05 9e 00 00 00 00  00 00 00 00 00 00 00 00  |e...............|
00000060  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
00000200

Now, after removing some files we can see that corresponding records still exist in directory:

# rm e d a
# hd .
00000000  00 14 01 00 0c 00 04 01  2e 00 00 00 02 00 00 00  |................|
00000010  18 00 04 02 2e 2e 00 00  01 14 01 00 0c 00 08 01  |................|
00000020  61 00 05 9e 02 14 01 00  0c 00 08 01 62 00 05 9e  |a...........b...|
00000030  03 14 01 00 d0 01 08 01  63 00 05 9e 04 14 01 00  |........c.......|
00000040  c4 01 08 01 64 00 05 9e  05 14 01 00 b8 01 08 01  |....d...........|
00000050  65 00 05 9e 00 00 00 00  00 00 00 00 00 00 00 00  |e...............|
00000060  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
00000200
# ls 
b       c

If we add some files, we can see that deleted record is used again:

# touch f 
# hd .
00000000  00 14 01 00 0c 00 04 01  2e 00 00 00 02 00 00 00  |................|
00000010  0c 00 04 02 2e 2e 00 00  01 14 01 00 0c 00 08 01  |................|
00000020  66 00 e9 05 02 14 01 00  0c 00 08 01 62 00 05 9e  |f...........b...|
00000030  03 14 01 00 d0 01 08 01  63 00 05 9e 04 14 01 00  |........c.......|
00000040  c4 01 08 01 64 00 05 9e  05 14 01 00 b8 01 08 01  |....d...........|
00000050  65 00 05 9e 00 00 00 00  00 00 00 00 00 00 00 00  |e...............|
00000060  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
00000200