DosTips :Format function truncating results

:: cont'd from http://www.dostips.com/forum/viewtopic.php?f=3&t=2891&p=13349#p13349
:: Here is the full script and output. It quits after processing the first loop:
@echo off
:showWinExe
  setlocal enabledelayedexpansion
  set string=arbitrary list of words that are at least this long in order to show truncation
  call :Format [-15][-15][-15] %string%
  goto :eof

:Format fmt str1 str2 ... -- outputs columns of strings right or left aligned
::                        -- fmt [in] - format string specifying column width and alignment, i.e. "[-10][10][10]"
:$created 20060101 :$changed 20091130 :$categories Echo
:$source http://www.dostips.com
SETLOCAL
set "fmt=%~1"
set "line="
set "spac=                                                     "
set "i=1"
echo. && echo. Recieved from caller: "%*" && echo.
for /f "tokens=1,2 delims=[" %%a in ('"echo..%fmt:]=&echo..%"') do (
    ECHO a = "[%%a]" : b = "[%%b]"
    set /a i+=1
    call call set "subst=%%%%~%%i%%%spac%%%%%~%%i%%"
    if %%b0 GEQ 0 (call set "subst=%%subst:~0,%%b%%"
    ) ELSE        (call set "subst=%%subst:~%%b%%")
    call set "const=%%a"
    call set "line=%%line%%%%const:~1%%%%subst%%"
    ECHO Loop number: %i%
)
echo.%line%
EXIT /b
:: ------------ end of file ------------------

:: output:
B:\code>format-test.bat

 Recieved from caller: "[-15][-15][-15] arbitrary list of words that are at least this long in order to show truncation"

a = "[.]" : b = "[-15]"
Loop number: 1
a = "[.]" : b = "[-15]"
Loop number: 1
a = "[.]" : b = "[-15]"
Loop number: 1
a = "[.]" : b = "[]"
Loop number: 1
      arbitrary           list             of
[/code]