windows 7 - Why does CMD substring not work when BAT called from SENDTO?

I wrote a BAT file to strip a leading '@' off a filename. (Please don't ask why! ...why Windows, why CMD...) :)

Here's the BAT file:

IF EXIST "%~1" (
    FOR /F %%F IN ("%~1") DO (
        CD /D "%%~dpF"
        IF ERRORLEVEL 1 (
            ECHO.  Failed to CD to folder: %%~dpF
        ) ELSE (
            SETLOCAL ENABLEEXTENSIONS
            SET A=%%~nxF
            IF "%A:~0,1%"=="@" (
                ECHO.   RENAME "%A%" "%A:~1%"
                    RENAME "%A%" "%A:~1%"
                REM   RENAME "%%A%" "%%A:~1%"
            ) ELSE (
                ECHO.   File does not start with @:  %A%
            )
            ENDLOCAL
        )
    )
) ELSE (
    ECHO.    File not found:  %1
)
pause

When I run it from the command line in a DOS window, it seems to work:

18:54:04.97>dir /b *foo*
@foo.txt
18:54:07.97>test@ "%cd%\@foo.txt"
18:54:18.75>IF EXIST "C:\Users\me\lbin\@foo.txt" (FOR /F %F IN ("C:\Users\me\lbin\@foo.txt") DO (
CD /D "%~dpF"
 IF ERRORLEVEL 1 (ECHO.  Failed to CD to folder: %~dpF )  ELSE (
SETLOCAL ENABLEEXTENSIONS
 SET A=%~nxF
 IF "@" == "@" (
ECHO.   RENAME "@foo.txt" "foo.txt"
 RENAME "@foo.txt" "foo.txt"
 REM   RENAME "%Afoo.txt"
)  ELSE (ECHO.   File does not start with @:  @foo.txt )
 ENDLOCAL
)
) )  ELSE (ECHO.    File not found:  "C:\Users\me\lbin\@foo.txt" )
18:54:18.77>(
CD /D "C:\Users\me\lbin\"
 IF ERRORLEVEL 1 (ECHO.  Failed to CD to folder: C:\Users\me\lbin\ )  ELSE (
SETLOCAL ENABLEEXTENSIONS
 SET A=@foo.txt
 IF "@" == "@" (
ECHO.   RENAME "@foo.txt" "foo.txt"
 RENAME "@foo.txt" "foo.txt"
 REM   RENAME "%Afoo.txt"
)  ELSE (ECHO.   File does not start with @:  @foo.txt )
 ENDLOCAL
)
)
   RENAME "@foo.txt" "foo.txt"
18:54:18.80>pause
Press any key to continue . . .
18:54:20.74>

but when I run the BAT file from a shortcut in the SENDTO menu, the substring operation doesn't expand correctly - specifically, the "IF" doesn't expand right (IF "%A:~0,1%"=="@" () - see?...

C:\Users\me\lbin>IF EXIST "C:\Users\me\lbin\@foo.txt" (FOR /F %F IN ("C:\Users\me\lbin\@foo.txt") D
O (
CD /D "%~dpF"
 IF ERRORLEVEL 1 (ECHO.  Failed to CD to folder: %~dpF )  ELSE (
SETLOCAL ENABLEEXTENSIONS
 SET A=%~nxF
 IF "~0,1" == "@" (
ECHO.   RENAME "" "~1"
 RENAME "" "~1"
 REM   RENAME "%A~1"
)  ELSE (ECHO.   File does not start with @:   )
 ENDLOCAL
)
) )  ELSE (ECHO.    File not found:  C:\Users\me\lbin\@foo.txt )
C:\Users\me\lbin>(
CD /D "C:\Users\me\lbin\"
 IF ERRORLEVEL 1 (ECHO.  Failed to CD to folder: C:\Users\me\lbin\ )  ELSE (
SETLOCAL ENABLEEXTENSIONS
 SET A=@foo.txt
 IF "~0,1" == "@" (
ECHO.   RENAME "" "~1"
 RENAME "" "~1"
 REM   RENAME "%A~1"
)  ELSE (ECHO.   File does not start with @:   )
 ENDLOCAL
)
)
   File does not start with @:
C:\Users\me\lbin>pause
Press any key to continue . . .

Ideas?