<?php

$str[] = "Makefile";
$str[] = "makefile";
$str[] = "..";
$str[] = "X-picturev";

$regexp = "^[a-z]";

while ( list( $key, $e) = each($str) ){

        if( ereg( $e, $regexp))
                echo "$e is lower<br>";
        else
                echo "$e is UPPER<br>";
}
?>

confugured --regex=pcre
http://tbiz.webrelay.net/test/ereg.php  will illustrate the 
bug and show phpinfo();

Also php4.0pl1 with OpenBSD with -regex=php will behave similarly.