Index: wp-admin/includes/screen.php
===================================================================
--- wp-admin/includes/screen.php	(revision 18887)
+++ wp-admin/includes/screen.php	(working copy)
@@ -724,21 +724,20 @@
 				$per_page = $this->_options['per_page']['default'];
 			else
 				$per_page = 20;
-		}
 
-		if ( 'edit_comments_per_page' == $option ) {
-			$comment_status = isset( $_REQUEST['comment_status'] ) ? $_REQUEST['comment_status'] : 'all';
-			$per_page = apply_filters( 'comments_per_page', $per_page, $comment_status );
-		} elseif ( 'categories_per_page' == $option ) {
-			$per_page = apply_filters( 'edit_categories_per_page', $per_page );
-		} else {
-			$per_page = apply_filters( $option, $per_page );
-		}
+			if ( 'edit_comments_per_page' == $option ) {
+				$comment_status = isset( $_REQUEST['comment_status'] ) ? $_REQUEST['comment_status'] : 'all';
+				$per_page = apply_filters( 'comments_per_page', $per_page, $comment_status );
+			} elseif ( 'categories_per_page' == $option ) {
+				$per_page = apply_filters( 'edit_categories_per_page', $per_page );
+			} else {
+				$per_page = apply_filters( $option, $per_page );
+			}
 
-		// Back compat
-		if ( isset( $this->post_type ) )
-			$per_page = apply_filters( 'edit_posts_per_page', $per_page, $this->post_type );
-
+			// Back compat
+			if ( isset( $this->post_type ) )
+				$per_page = apply_filters( 'edit_posts_per_page', $per_page, $this->post_type );
+		}
 		?>
 		<h5><?php _ex('Show on screen', 'Screen Options') ?></h5>
 		<div class='screen-options'>