Index: admin.php
===================================================================
--- admin.php	(revision 12371)
+++ admin.php	(working copy)
@@ -48,7 +48,6 @@
 
 set_screen_options();
 
-$posts_per_page = get_option('posts_per_page');
 $date_format = get_option('date_format');
 $time_format = get_option('time_format');
 
Index: categories.php
===================================================================
--- categories.php	(revision 12371)
+++ categories.php	(working copy)
@@ -166,10 +166,10 @@
 if ( empty($pagenum) )
 	$pagenum = 1;
 
-$cats_per_page = get_user_option('categories_per_page');
-if ( empty($cats_per_page) )
+$cats_per_page = (int) get_user_option( 'categories_per_page', 0, false );
+if ( empty( $cats_per_page ) || $cats_per_page < 1 )
 	$cats_per_page = 20;
-$cats_per_page = apply_filters('edit_categories_per_page', $cats_per_page);
+$cats_per_page = apply_filters( 'edit_categories_per_page', $cats_per_page );
 
 if ( !empty($_GET['s']) )
 	$num_cats = count(get_categories(array('hide_empty' => 0, 'search' => $_GET['s'])));
Index: edit-comments.php
===================================================================
--- edit-comments.php	(revision 12371)
+++ edit-comments.php	(working copy)
@@ -236,10 +236,10 @@
 </p>
 
 <?php
-$comments_per_page = get_user_option('edit_comments_per_page');
-if ( empty($comments_per_page) )
+$comments_per_page = (int) get_user_option( 'edit_comments_per_page', 0, false );
+if ( empty( $comments_per_page ) || $comments_per_page < 1 )
 	$comments_per_page = 20;
-$comments_per_page = apply_filters('comments_per_page', $comments_per_page, $comment_status);
+$comments_per_page = apply_filters( 'comments_per_page', $comments_per_page, $comment_status );
 
 if ( isset( $_GET['apage'] ) )
 	$page = abs( (int) $_GET['apage'] );
Index: edit-pages.php
===================================================================
--- edit-pages.php	(revision 12371)
+++ edit-pages.php	(working copy)
@@ -228,9 +228,10 @@
 $pagenum = isset( $_GET['pagenum'] ) ? absint( $_GET['pagenum'] ) : 0;
 if ( empty($pagenum) )
 	$pagenum = 1;
-$per_page = get_user_option('edit_pages_per_page');
-if ( empty( $per_page ) || $per_page < 0 )
+$per_page = (int) get_user_option( 'edit_pages_per_page', 0, false );
+if ( empty( $per_page ) || $per_page < 1 )
 	$per_page = 20;
+$per_page = apply_filters( 'edit_pages_per_page', $per_page );
 
 $num_pages = ceil($wp_query->post_count / $per_page);
 $page_links = paginate_links( array(
Index: edit-tags.php
===================================================================
--- edit-tags.php	(revision 12371)
+++ edit-tags.php	(working copy)
@@ -184,11 +184,11 @@
 if ( empty($pagenum) )
 	$pagenum = 1;
 
-$tags_per_page = get_user_option('edit_tags_per_page');
-if ( empty($tags_per_page) )
+$tags_per_page = (int) get_user_option( 'edit_tags_per_page', 0, false );
+if ( empty($tags_per_page) || $tags_per_page < 1 )
 	$tags_per_page = 20;
-$tags_per_page = apply_filters('edit_tags_per_page', $tags_per_page);
-$tags_per_page = apply_filters('tagsperpage', $tags_per_page); // Old filter
+$tags_per_page = apply_filters( 'edit_tags_per_page', $tags_per_page );
+$tags_per_page = apply_filters( 'tagsperpage', $tags_per_page ); // Old filter
 
 $page_links = paginate_links( array(
 	'base' => add_query_arg( 'pagenum', '%#%' ),
Index: includes/post.php
===================================================================
--- includes/post.php	(revision 12371)
+++ includes/post.php	(working copy)
@@ -845,10 +845,10 @@
 		$orderby = 'date';
 	}
 
-	$posts_per_page = get_user_option('edit_per_page');
-	if ( empty($posts_per_page) )
+	$posts_per_page = (int) get_user_option( 'edit_per_page', 0, false );
+	if ( empty( $posts_per_page ) || $posts_per_page < 1 )
 		$posts_per_page = 15;
-	$posts_per_page = apply_filters('edit_posts_per_page', $posts_per_page);
+	$posts_per_page = apply_filters( 'edit_posts_per_page', $posts_per_page );
 
 	wp("post_type=post&$post_status_q&posts_per_page=$posts_per_page&order=$order&orderby=$orderby");
 
@@ -903,10 +903,10 @@
 	$q['cat'] = isset( $q['cat'] ) ? (int) $q['cat'] : 0;
 	$q['post_type'] = 'attachment';
 	$q['post_status'] = isset( $q['status'] ) && 'trash' == $q['status'] ? 'trash' : 'inherit';
-	$media_per_page = get_user_option('upload_per_page');
-	if ( empty($media_per_page) )
+	$media_per_page = (int) get_user_option( 'upload_per_page', 0, false );
+	if ( empty( $media_per_page ) || $media_per_page < 1 )
 		$media_per_page = 20;
-	$q['posts_per_page'] = $media_per_page;
+	$q['posts_per_page'] = apply_filters( 'upload_per_page', $media_per_page );
 
 	$post_mime_types = get_post_mime_types();
 	$avail_post_mime_types = get_available_post_mime_types('attachment');
Index: includes/template.php
===================================================================
--- includes/template.php	(revision 12371)
+++ includes/template.php	(working copy)
@@ -3716,14 +3716,20 @@
 			return '';
 	}
 
-	$option = str_replace('-', '_', "${screen}_per_page");
-	$per_page = get_user_option($option);
-	if ( empty($per_page) ) {
+	$option = str_replace( '-', '_', "${screen}_per_page" );
+	$per_page = (int) get_user_option( $option, 0, false );
+	if ( empty( $per_page ) || $per_page < 1 ) {
 		if ( 'plugins' == $screen )
 			$per_page = 999;
 		else
 			$per_page = 20;
 	}
+	if ( 'edit_comments_per_page' == $option )
+		$per_page = apply_filters( 'comments_per_page', $per_page, isset($_REQUEST['comment_status']) ? $_REQUEST['comment_status'] : 'all' );
+	elseif ( 'categories' == $option )
+		$per_page = apply_filters( 'edit_categories_per_page', $per_page );
+	else
+		$per_page = apply_filters( $option, $per_page );
 
 	$return = '<h5>' . __('Options') . "</h5>\n";
 	$return .= "<div class='screen-options'>\n";
Index: plugins.php
===================================================================
--- plugins.php	(revision 12371)
+++ plugins.php	(working copy)
@@ -350,10 +350,10 @@
 //Paging.
 $total_this_page = "total_{$status}_plugins";
 $total_this_page = $$total_this_page;
-$plugins_per_page = get_user_option('plugins_per_page');
-if ( empty($plugins_per_page) )
+$plugins_per_page = (int) get_user_option( 'plugins_per_page', 0, false );
+if ( empty( $plugins_per_page ) || $plugins_per_page < 1 )
 	$plugins_per_page = 999;
-$plugins_per_page = apply_filters('plugins_per_page', $plugins_per_page);
+$plugins_per_page = apply_filters( 'plugins_per_page', $plugins_per_page );
 
 $start = ($page - 1) * $plugins_per_page;
 
Index: upload.php
===================================================================
--- upload.php	(revision 12371)
+++ upload.php	(working copy)
@@ -134,9 +134,10 @@
 
 if ( isset($_GET['detached']) ) {
 
-	$media_per_page = (int) get_user_option('upload_per_page');
-	if ( empty($media_per_page) )
+	$media_per_page = (int) get_user_option( 'upload_per_page', 0, false );
+	if ( empty($media_per_page) || $media_per_page < 1 )
 		$media_per_page = 20;
+	$media_per_page = apply_filters( 'upload_per_page', $media_per_page );
 
 	if ( !empty($lost) ) {
 		$start = ( (int) $_GET['paged'] - 1 ) * $media_per_page;