Description of Problem:
This problem has been verified with nautilus 2.4.1
as shipped in debian unstable. I apologize but I
couldn't test it with 2.5.2 .
I set LANG="en_US.UTF-8" but still had files with
an Umlaut in it from a former de_DE installation.
Nautilus correctly displays a warning "(invalid
Unicode)" after the filename. The problem is, when
you rename the file, this warning becomes part of
the filename.

Steps to reproduce the problem:
1. export LANG="en_US" and start an xterm. Then
create a filename with an umlaut in it.
2. export LANG="en_US.UTF-8" and go to that
folder. It will display the filename with
"(invalid Unicode)" after it. 
3. Rename the file and the warning will become
part of the filename, which should be verified in
a shell because inside nautilus it looks just the
same.

Expected Results:
The warning should be removed when nautilus
displays an text field so you can edit the filename.

How often does this happen? 
It always happens. 

Additional Information: