Index: wp-admin/includes/post.php
===================================================================
--- wp-admin/includes/post.php	(revision 17942)
+++ wp-admin/includes/post.php	(working copy)
@@ -1284,6 +1284,17 @@
 }
 
 /**
+ * Outputs the notice message to say that this page is used for posts and content will be ignored.
+ *
+ * @since 3.2
+ * @return none
+ */
+function _admin_notice_page_for_posts() {
+	$message = __( 'This page is used to display a list of posts; content here will not be displayed. You can change this in your <a href="%s">Reading Settings</a>.' );
+	echo '<div class="error"><p>' . sprintf( $message, esc_url( admin_url( 'options-reading.php' ) ) ) . '</p></div>';
+}
+
+/**
  * Creates autosave data for the specified post from $_POST data.
  *
  * @package WordPress
Index: wp-admin/post.php
===================================================================
--- wp-admin/post.php	(revision 17942)
+++ wp-admin/post.php	(working copy)
@@ -176,6 +176,10 @@
 		wp_enqueue_script('autosave');
 	}
 
+	if ( $post_id == get_option( 'page_for_posts' ) ) {
+		add_action( 'admin_notices', '_admin_notice_page_for_posts' );
+	}
+
 	$title = $post_type_object->labels->edit_item;
 	$post = get_post_to_edit($post_id);