I have this code on my website that occasionally will log users in and occasionally just redirect to the wordpress login page. Additionally, if a field was left blank it would actually show errors on the wordpress login page, but now it just does a redirect.
<form id="wp_login_form" action="<?php echo site_url('/wp-login.php', 'https') ?>" method="post">
<div class="formrow">
<div class="formLabel"><label for="log">Email </label></div>
<div class="forminput"><input type="text" name="log" id="log" value="<?php echo wp_specialchars(stripslashes($user_login), 1) ?>" size="25" /></div>
</div>
<div class="formrow">
<div class="formLabel"><label for="pwd"><?php _e('Password') ?> </label></div>
<div class="forminput"><input type="password" name="pwd" id="pwd" size="25" autocomplete="off" /></div>
</div>
<div class="formrow lowercase">
<div class="formLabel"></div>
<div class="forminput"><label for="rememberme"><input name="rememberme" type="checkbox" id="rememberme" value="forever" <?php checked( $rememberme ); ?> /> <?php esc_attr_e('Remember Me'); ?></label></div>
</div>
<div class="formrow">
<div class="forminput"><input type="submit" name="submit" value="<?php esc_attr_e('Log In'); ?>" class="button" /></div>
<input type="hidden" name="redirect_to" value="<?php echo $_SERVER['REQUEST_URI']; ?>"/>
</div>
<div class="formrow">
<div class="forminput lowercase"><a href="<?php echo get_option('home'); ?>/wp-login.php?action=lostpassword">Forgot password?</a></div>
</div>
</form>
