I am expecting that a number with a base X is converted to itself if the base is unchanged.

<?php

$number = "987654321";
$after  = base_convert($number, 10, 10);

echo "\nBefore: $number";
echo "\nAfter : $after\n\n";

?>

987654321 gives back, in fact, 987654321.

Unfortunately, this is not always true:

<?php

$number = "9876543210";
$after  = base_convert($number, 10, 10);

echo "\nBefore: $number";
echo "\nAfter : $after\n\n";

?>

9876543210 gives back 1286608618

The 4.2.3 version I have been using is the one that comes with the Mandrake 9.0 distribution.
I have been keeping it regularly updated on the web (now is Dec 12th, 2002).