Please try using this CVS snapshot:

  http://snaps.php.net/php5-latest.tar.gz
 
For Windows:
 
  http://snaps.php.net/win32/php5-win32-latest.zip

Dear sir,

Thanks for your help. I have test it in a php 5.1.X version. But the bug doesn't fixed. The meaningless space change to a square characters only...

Anyway, thanks for your help. (This problem hasn't exist in Excel, it only happened in Word only)

From Victor

Assigned to the maintainer of COM extension.

I am experiencing the same bug with Arabic - I pull a UTF-8 character from a database, and push it into Word with UTF-8 for the characterset. I get meaningless characters (the box) appearing after (to the right of) the arabic text. Also, the arabic text gets mangled - words out of order...

I would try to post the input/output here, but it would be meaningless...

Make sure you're setting up the code page properly.
From the manual:

com.code_page

    It controls the default character set code-page to use when passing strings to and from COM objects. If set to an empty string, PHP will assume that you want CP_ACP, which is the default system ANSI code page.

    If the text in your scripts is encoded using a different encoding/character set by default, setting this directive will save you from having to pass the code page as a parameter to the COM class constructor. Please note that by using this directive (as with any PHP configuration directive), your PHP script becomes less portable; you should use the COM constructor parameter whenever possible.

Consult MSDN for more information on code pages.

After yours information, I have try to modified my code and make it support the correct code_page. But finially the result is exactly the same with my first script. There are some meaningless square appears after my Chinese word. (Actually I'm quite confused that why only Word has this problem but excel didn't?)

here are some link related to this problem:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/act/htm/actml_ref_scpg.asp
http://bugs.php.net/bug.php?id=31327
http://bugs.php.net/bug.php?id=28117
http://hk.php.net/manual/en/class.com.php

here are my new scripts:
<?php

$code_page=array('950','0','1','2','3','65001');

for ($i=0;$i<count($code_page);$i++){
    // starting word
    $word = new COM("word.application",NULL,$code_page[$i]) or die("Unable to instantiate Word");
    echo "Loaded Word, version {$word->Version}\n";
    
    //bring it to front
    $word->Visible = 1;
    
    //open an empty document
    $word->Documents->Add();
    
    //do some weird stuff
    $word->Selection->TypeText("???Æ?");
    $word->Documents[1]->SaveAs("D:\AppServ\www\word\\".$code_page[$i].".doc");
    
    //closing word
    $word->Quit();
    
    //free the object
    $word = null;
}    
?>

I have see the lastest version of php 5.0.5 and 5.1
but the change log haven't mention about this bug has been fixed. So would you tell me the developer doesn't think that this is a bug so they will not fix it or they are try to fixing it but didn't finish yet?

When I upgraded PHP to 5.2.0, this problem still exists.
Several "encoding-traslate" codes don't make effect.

Windows Server 2003 R2 SP2
Apache 2
Office 2003 SP2

I think I'm experiencing the same problem, but I'm not sure because I can't see the original problem text on this page.  

I have documented my problem on StackOverflow with simple code to reproduce: http://stackoverflow.com/questions/28534219/writing-utf-8-strings-to-word-using-php-com 

Environment: I'm using Windows 7 Enterprise, Apache, MySQL, PHP 5.2.17, and Microsoft Office 2010.

It seems like the string length is not calculated correctly (using bytes and not characters), resulting in a longer string with garbage at the end.

@katszym:
See bug #66431. Looks like it was fixed in PHP 5.4.29.