This is a really strange problem, but sprintf seems to be padding a null character to the end of a string when the string consists of a negative float. Here is a script that will reproduce the problem:

<?

$string = -122.440383;
$new_string = sprintf("%0.6f", $string);
echo "string = $string<br>\n";
echo "new_string = $new_string<br>\n";
for ($j=0;$j<strlen($new_string);$j++) {
    echo "letter #$j: " . ord($new_string[$j]) . "<br>\n";
}

?>

The output on php-3.0.14, php-3.0.13, php-4.0b3 looks like:
string = -122.440383
new_string = -122.440383
letter #0: 45
letter #1: 49
letter #2: 50
letter #3: 50
letter #4: 46
letter #5: 52
letter #6: 52
letter #7: 48
letter #8: 51
letter #9: 56
letter #10: 51
letter #11: 0

There is no null character at the end if the float is positive.

I noticed that php-3.0.12 doens't exhibit this behavior. The way I configured all these different versions of php was:

Configure command: ./configure '--with-mhash' '--with-mcrypt' '--disable-display-source' '--enable-debugger' '--enable-track-vars' '--enable-debug' '--with-xml' '--with-oracle' '--without-gd' '--with-apxs=../www/bin/apxs'

The one major difference I know between my versions of php-3.0.12 and the others is that 3.0.12 compiles against an older version of mcrypt and all these others compile against a newwr version. This is probably irrelevant because I have no idea what mcrypt libraries would have to do with sprintf, but I thought I'd mention it.

Thanks.

-Greg