If this isn't a bug it's certainly a major OS X shortcoming. (The first time it happened I thought I had for sure misremembered what I had done, but it's reproducible.)

While booted into my SL volume I did a CCC file-level clone and a DU file-level "Restore" of the volume into which I was booted, with these results:

Code:
Source:
Artie-s-Computer-4:~ artie$ sudo du -xhd1 /
Password:
4.0M	/.fseventsd
4.0K	/.Spotlight-V100
  0B	/.Trashes
  0B	/.vol
902M	/Applications
3.9M	/bin
  0B	/cores
4.5K	/dev
1.0K	/home
1.5G	/Library
1.0K	/net
  0B	/Network
746M	/private
2.6M	/sbin
1.7G	/System
155M	/Users
392M	/usr
4.0K	/Volumes
5.4G	/
Artie-s-Computer-4:~ artie$

Code:
Destination (CCC clone):
Artie-s-Computer-4:~ artie$ sudo du -xhd1 /
Password:
416K	/.fseventsd
 39M	/.Spotlight-V100
  0B	/.Trashes
  0B	/.vol
902M	/Applications
3.9M	/bin
  0B	/cores
4.5K	/dev
1.0K	/home
1.5G	/Library
1.0K	/net
  0B	/Network
745M	/private
2.6M	/sbin
1.7G	/System
155M	/Users
392M	/usr
4.0K	/Volumes
5.4G	/
Artie-s-Computer-4:~ artie$ 
(Elapsed time: 00:11:54)

Code:
Destination (DU "Restore"):
Artie-s-Computer-4:~ artie$ sudo du -xhd1 /
4.4M	/.fseventsd
 36M	/.Spotlight-V100
  0B	/.Trashes
  0B	/.vol
1014M	/Applications
9.0M	/bin
  0B	/cores
4.5K	/dev
1.0K	/home
1.6G	/Library
1.0K	/net
  0B	/Network
220M	/private
6.8M	/sbin
3.4G	/System
155M	/Users
937M	/usr
4.0K	/Volumes
7.3G	/
Artie-s-Computer-4:~ artie$ 
(Restore took 15 minutes)

and, by way of example:

Code:
Destination (CCC clone):
Artie-s-Computer-4:~ artie$ /Volumes/HD2/3rd\ Party\ Stuff/Apps/Pacifist/hfs_comp_tool /bin/*
File /bin/[ is compressed
File /bin/bash is compressed
File /bin/cat is compressed
File /bin/chmod is compressed
File /bin/cp is compressed
File /bin/csh is compressed
File /bin/date is compressed
File /bin/dd is compressed
File /bin/df is compressed
File /bin/domainname is compressed
File /bin/echo is compressed
File /bin/ed is compressed
File /bin/expr is compressed
File /bin/hostname is compressed
File /bin/kill is compressed
File /bin/ksh is compressed
File /bin/launchctl is compressed
File /bin/link is compressed
File /bin/ln is compressed
File /bin/ls is compressed
File /bin/mkdir is compressed
File /bin/mv is compressed
File /bin/pax is compressed
File /bin/ps is compressed
File /bin/pwd is compressed
File /bin/rcp is compressed
File /bin/rm is compressed
File /bin/rmdir is compressed
File /bin/sh is compressed
File /bin/sleep is compressed
File /bin/stty is compressed
File /bin/sync is compressed
File /bin/tcsh is compressed
File /bin/test is compressed
File /bin/unlink is compressed
File /bin/wait4path is compressed
File /bin/zsh is compressed
Artie-s-Computer-4:~ artie$

Code:
Destination (DU "Restore"):
Artie-s-Computer-4:~ artie$ /Volumes/HD2/3rd\ Party\ Stuff/Apps/Pacifist/hfs_comp_tool /bin/*
File /bin/[ is not compressed
File /bin/bash is not compressed
File /bin/cat is not compressed
File /bin/chmod is not compressed
File /bin/cp is not compressed
File /bin/csh is not compressed
File /bin/date is not compressed
File /bin/dd is not compressed
File /bin/df is not compressed
File /bin/domainname is not compressed
File /bin/echo is not compressed
File /bin/ed is not compressed
File /bin/expr is not compressed
File /bin/hostname is not compressed
File /bin/kill is not compressed
File /bin/ksh is not compressed
File /bin/launchctl is not compressed
File /bin/link is not compressed
File /bin/ln is not compressed
File /bin/ls is not compressed
File /bin/mkdir is not compressed
File /bin/mv is not compressed
File /bin/pax is not compressed
File /bin/ps is not compressed
File /bin/pwd is not compressed
File /bin/rcp is not compressed
File /bin/rm is not compressed
File /bin/rmdir is not compressed
File /bin/sh is not compressed
File /bin/sleep is not compressed
File /bin/stty is not compressed
File /bin/sync is not compressed
File /bin/tcsh is not compressed
File /bin/test is not compressed
File /bin/unlink is not compressed
File /bin/wait4path is not compressed
File /bin/zsh is not compressed
Artie-s-Computer-4:~ artie$

CCC retains compression...DU does not.

Hmmm...

The new Great Equalizer is the SEND button.

In Memory of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire