Index: wp-admin/includes/template.php
===================================================================
--- wp-admin/includes/template.php	(revision 8176)
+++ wp-admin/includes/template.php	(working copy)
@@ -915,7 +915,7 @@
 	</tr>
 <tr class="submit"><td colspan="3">
 	<?php wp_nonce_field( 'add-meta', '_ajax_nonce', false ); ?>
-	<input type="submit" id="addmetasub" name="addmeta" class="add:the-list:newmeta::post_id=<?php echo $GLOBALS['post_ID'] ? $GLOBALS['post_ID'] : $GLOBALS['temp_ID']; ?>" tabindex="9" value="<?php _e( 'Add Custom Field' ) ?>" />
+	<input type="submit" id="addmetasub" name="addmeta" class="add:the-list:newmeta" tabindex="9" value="<?php _e( 'Add Custom Field' ) ?>" />
 </td></tr>
 </table>
 <?php
Index: wp-admin/js/post.js
===================================================================
--- wp-admin/js/post.js	(revision 8176)
+++ wp-admin/js/post.js	(working copy)
@@ -181,5 +181,9 @@
 		if ( jQuery.isFunction( autosave_update_post_ID ) ) {
 			autosave_update_post_ID(s.parsed.responses[0].supplemental.postid);
 		}
-	} });
+	}, addBefore: function( s ) {
+		s.data += '&post_id=' + jQuery('#post_ID').val();
+		return s;
+	}
+	});
 });