When you 'force' a move to the same filename (by accident)
it will unlink the file... here is the log:

root@zeppelin:[ /tmp/test ] l
total 0
root@zeppelin:[ /tmp/test ] echo > test
root@zeppelin:[ /tmp/test ] l
total 1
   1 -rw-r--r--   1 root     root            1 May 22 22:53
test
root@zeppelin:[ /tmp/test ] /bin/mv test test
/bin/mv: `test' and `test' are the same file
root@zeppelin:[ /tmp/test ] l
total 1
   1 -rw-r--r--   1 root     root            1 May 22 22:53
test
root@zeppelin:[ /tmp/test ] /bin/mv -f test test
/bin/mv: `test' and `test' are the same file
root@zeppelin:[ /tmp/test ] l
total 0