Fossil undo doesn't work after a mv/ren operation.  Also, I'm unable to move the file back up the source tree because fossil thinks the path is outside of the checkout tree.  I tried several variations.  Here is my repro on Windows 7 using PowerShell:
<pre>
PS fossil ver
This is fossil version [7aae4ef068] 2010-09-03 01:57:41 UTC
PS fossil new ..\test.fossil
project-id:
server-id:
admin-user: rwilso20 (initial password is "670296")
PS fossil open ..\test.fossil
PS ls


    Directory:


Mode                LastWriteTime     Length Name
----                -------------     ------ ----
-a---         11:18 AM       7168 _FOSSIL_


PS echo 123 > x.txt
PS fossil add .\x.txt
ADDED  x.txt
PS fossil commit -m "1"
New_Version:
PS md sub


    Directory:


Mode                LastWriteTime     Length Name
----                -------------     ------ ----
d----         11:20 AM            sub


PS fossil mv .\x.txt sub
RENAME x.txt sub/x.txt
PS fossil undo
no update or merge operation is available to undo
PS move x.txt sub
PS fossil mv .
file outside of checkout tree: .
PS fossil mv .\
file outside of checkout tree: .\
PS fossil commit -m "2"
New_Version:
PS ls


    Directory:


Mode                LastWriteTime     Length Name
----                -------------     ------ ----
d----         11:21 AM            sub
-a---         11:24 AM        211 manifest
-a---         11:24 AM         41 manifest.uuid
-a---         11:24 AM       8192 _FOSSIL_


PS fossil mv .
file outside of checkout tree: .
PS fossil mv .\
file outside of checkout tree: .\
PS
</pre>