Before this ini parameter was introduced the default behavior of the extension was to convvert the dates. If we changed this we would break a lot of code.

The default behavior also breaks a lot of code, I dare say including PEAR. Consider the following example:

<?php

require_once "DB.php";

$db = DB::connect("mssql://user:pass@localhost/db");

$sql = "SELECT {fn NOW()}";
$date = $db->getOne($sql);

echo "NOW() is $date<br />";

$sql = "SELECT CAST('$date' AS DATETIME)";
$date = $db->getOne($sql);

if (DB::isError($date)) {
  echo $date->toString();
}
else {
  echo "The date is $date";
}
?>


Now, the only reasonable outcome of this code would be to print the same date twice, regardless of which format it was initially... right?

Well, no. Here's what I get from running this code:

NOW() is 14 maj 2003 9:03
[db_error: message="DB Error: " code=-1 mode=return level=notice prefix="" info="SELECT CAST('14 maj 2003 9:03' AS DATETIME) [nativecode=Syntax error converting datetime from character string.]"]

Switch the SELECT CAST() for an INSERT statement and you'll realize why this is dangerous. It works for ten months of the year, and breaks in May (maj) and October (oktober). Different host languages will cause the code to work or fail in different months.

Yes, I realize that changing this behaviour would also affect a lot of existing code. But this would mostly be a cosmetical change, unless the existing code is completely dependent on parsing the date as a string. But as I can tell you first-hand, trying to explain to a customer why their code suddenly stopped working by the turn of May without us changing anything is _not_ my idea of fun.

Testing without PEAR does not give me any errors. This is my code

<?php

dl("php_mssql.dll");

$con = mssql_connect("local", "user", "pass");

$result=mssql_query("SELECT {fn NOW()}");
$row = mssql_fetch_row($result);
print_r($row);

$date = $row[0];
$result1=mssql_query("SELECT CAST('$date' AS DATETIME)");
$row1 = mssql_fetch_row($result1);
print_r($row1);

?>

and the output
Array
(
    [0] => May 14 2003  5:15PM
)
Array
(
    [0] => May 14 2003  5:15PM
)

I would say this is a server configuration problem. specific to your local settings. Wow did you create the alias (Client Network Utility) and what is the value of the different options you can configure ?
 

We've noticed that under some circumstances the php_mssql extensions seems to switch the mssql.datetimeconvert flag setting between On and Off. Most of the time we get the date in the Off format (cause we've set the flag to Off in the ini file), i.e. YYYY-MM-DD HH:MM:SS, but sometimes it switch to On wich will give us the format "14 maj 2003 9:03" and the db inseret query failes.
Is there any patches for php_mssql module? 
Anyone seen this problem before? Solution?
Platform is Win2k Server, MSSQL 2000, PHP 4.3.1.

I've managed to encounter this quirk with our development team running identical 
hardware / operating systems (Windows XP) and identical versions of PHP 5.4.9 and 
MSSQL extensions.

And yet, on one machine the php.ini had the option commented out (defaults to On) 
and on the other it was uncommented and set to Off.

With MSSQL being removed from PHP as of PHP7.0, and ext/mssql not having a maintainer, I'm gonna close this report as a Won't fix, until maybe one day it will find a new maintainer.

Alternatively you can use sqlsrv from Microsoft if you are on Windows, or pdo_dblib if you are on Unix.