Index: src/wp-admin/includes/class-wp-media-list-table.php
===================================================================
--- src/wp-admin/includes/class-wp-media-list-table.php	(revision 32504)
+++ src/wp-admin/includes/class-wp-media-list-table.php	(working copy)
@@ -259,12 +259,17 @@
 	}
 
 	protected function get_sortable_columns() {
+
+		// the initial sorting is by date and descending
+		// in the initial view the order on first click on 'Date' should be 'asc'
+		$desc_first = isset( $_GET['orderby'] ) ? true : false;
+
 		return array(
 			'title'    => 'title',
 			'author'   => 'author',
 			'parent'   => 'parent',
 			'comments' => 'comment_count',
-			'date'     => array( 'date', true ),
+			'date'     => array( 'date', $desc_first ),
 		);
 	}
 
Index: src/wp-admin/includes/class-wp-users-list-table.php
===================================================================
--- src/wp-admin/includes/class-wp-users-list-table.php	(revision 32504)
+++ src/wp-admin/includes/class-wp-users-list-table.php	(working copy)
@@ -281,8 +281,13 @@
 	 * @return array Array of sortable columns.
 	 */
 	protected function get_sortable_columns() {
+
+		// the initial sorting is by username ('login') and ascending
+		// in the initial view the order on first click on 'Username' should be 'desc'
+		$desc_first = isset( $_GET['orderby'] ) ? false : true;
+
 		$c = array(
-			'username' => 'login',
+			'username' => array( 'login', $desc_first ),
 			'name'     => 'name',
 			'email'    => 'email',
 		);