The curious case of the missing exclamation mark in CMD files

I have whittled down a more complex CMD script to the essentials. It reads an input file line by line, unquotes it (if quoted) and writes it out to another CMD file.

The problem is that if the input file contains exclamation marks (! or bang) the character gets stripped out somewhere along the line.

Here is the CMD script, BANG1.CMD:

@echo off
setlocal ENABLEEXTENSIONS ENABLEDELAYEDEXPANSION
if exist bang2.cmd del bang2.cmd
for /f "tokens=*" %%a in (bang1.txt) do call :doit1 %%a
exit /b

:doit1
set P1=%1
if %P1%. EQU . exit /b
call :unquotex P1 %P1%
echo>>bang2.cmd echo P1:[%P1%]
exit /b

:unquotex
set X=%2
set Q=%X:~0,1%
if "!Q!" EQU ^""" SET X=!X:~1,-1!
set %1=%X%
exit /b

Here is the input file BANG1.TXT:

HelloWorld
"Hello World"
Hello!World
"Hello!World"

The resulting file BANG2.CMD ends up containing this:

echo P1:[HelloWorld]
echo P1:[Hello World]
echo P1:[HelloWorld]
echo P1:[HelloWorld]

The question is, what happened to the embedded bangs? I have tried with and without ENABLEDELAYEDEXPANSION. I have even tried escaping (^) the bangs in the input file, still with no luck.

Is there any way to preserve them?

Thanks.