Please try using this CVS snapshot:

  http://snaps.php.net/php5.2-latest.tar.gz
 
For Windows:
 
  http://snaps.php.net/win32/php5.2-win32-latest.zip

I've tried the link for Windows you suggested: http://snaps.php.net/win32/php5.2-win32-latest.zip.
Now i've this version of php: "PHP Version 5.2.1RC2-dev".

But the problem isn't resolved. On the contrary, it's going worse: now it's ignored also the decimal separator [decimal_point] with %f.
The problem persists also with other os.
With the same script of the previous message, here it is the output produced:

Actual result:
--------------
Italian_Italy.1252
1234,56
 Not dependant in local settings: 1234.56000 

 Dependant on local settings: 1234.560000 
Array
(
    [decimal_point] => ,
    [thousands_sep] => .

    ...etc...

)

The expected result is obviously the same as the previous message:
Expected result:
----------------
Italian_Italy.1252
1.234,56
 Not dependant in local settings: 1234.560000 

 Dependant on local settings: 1.234,560000 
Array
(
    [decimal_point] => ,
    [thousands_sep] => .

    ...etc...

)

>But the problem isn't resolved. 
Yes, it was never supposed to work this way.
This is exactly the reason why wer have number_format() function.

>On the contrary, it's going worse:
I can't reproduce this.
Please try the next snapshot.

> Yes, it was never supposed to work this way.
> This is exactly the reason why wer have number_format() 
> function.

I don't think so.
If I see, in localeconv():
    [decimal_point] => ,
    [thousands_sep] => .

I expect that the number formatted with:
printf("%f",$num)

is 1.234,56 and NOT 1234,56

As you can see the [decimal_point] is ",", according with localeconv(), but the [thousands_sep] doesn't appear here, disaccording with localeconv().

The manual states about the %f:
"f - the argument is treated as a float, and presented as a floating-point number (locale aware)."

But in this case the locale aware is not respected: it's respected only for [decimal_point] and NOT for [thousands_sep].

>> On the contrary, it's going worse:
> I can't reproduce this.
> Please try the next snapshot.

For:
printf("%f",$num)
before it produced (with loca setted on "it"):
"1234,56"
now it incorrectly produces:
"1234.56"
that is it forgets both the [thousands_sep] AND the [decimal_point].

>I don't think so.
>If I see, in localeconv():
>I expect that the number formatted with:

That does not mean it was supposed to work the way you expect.

>But in this case the locale aware is not respected: it's
> respected only for [decimal_point] and NOT for
> [thousands_sep].
Right, that's how it is supposed to work and it should be clarified in the docs.

>now it incorrectly produces:
Again, please try the NEXT snapshot, I'm unableto reproduce it.

> That does not mean it was supposed to work the way you 
> expect.
> it should be clarified in the docs.

Yes, if this is the way it works, it should be clarified in docs.

> please try the NEXT snapshot, I'm unableto reproduce it.

I've tried the last available snapshot. 
Here is the problem:

Reproduce code:
---------------
<?php
$ita=array("ita","it","Italian","it_IT","it_IT.ISO8859-1","it_IT.ISO_8859-1");
setlocale(LC_ALL,$ita);

$num=0+"1234.56";  

$formatted_num=number_format($num,2);
echo $formatted_num;
?>

Expected result:
----------------
1,234.56

Actual result:
--------------
1,234,,56.00

it sounds quite strange...:-)

This bug has been fixed in CVS.

Snapshots of the sources are packaged every three hours; this change
will be in the next snapshot. You can grab the snapshot at
http://snaps.php.net/.
 
Thank you for the report, and for helping us make PHP better.