Index: src/wp-includes/js/tinymce/plugins/wordpress/plugin.js
===================================================================
--- src/wp-includes/js/tinymce/plugins/wordpress/plugin.js	(revision 36805)
+++ src/wp-includes/js/tinymce/plugins/wordpress/plugin.js	(working copy)
@@ -566,8 +566,23 @@
 				wp.autosave.server.triggerSave();
 			}
 		} );
+
+		if ( window.getUserSetting( 'editor_plain_text_paste_warning' ) > 1 ) {
+			editor.settings.paste_plaintext_inform = false;
+		}
 	} );
 
+	editor.on( 'PastePlainTextToggle', function( event ) {
+		// Warn twice, then stop.
+		if ( event.state === true ) {
+			var times = parseInt( window.getUserSetting( 'editor_plain_text_paste_warning' ), 10 ) || 0;
+
+			if ( times < 2 ) {
+				window.setUserSetting( 'editor_plain_text_paste_warning', ++times );
+			}
+		}
+	});
+
 	/**
 	 * Experimental: create a floating toolbar.
 	 * This functionality will change in the next releases. Not recommended for use by plugins.