Autocomplete: Do not set value on multi-line input

This fixes an issue where contenteditable text was getting overwritten when
wrapping past the bottom or top of the autocomplete menu.

Fixes #9771
Closes gh-1184

tests/unit/autocomplete/autocomplete_core.js

@@ -163,6 +163,32 @@ test( "allow form submit on enter when menu is not active", function() {
 	}
 })();
 
+asyncTest( "past end of menu in multiline autocomplete", function() {
+	expect( 2 );
+
+	var customVal = "custom value",
+		element = $( "#autocomplete-contenteditable" ).autocomplete({
+			delay: 0,
+			source: [ "javascript" ],
+			focus: function( event, ui ) {
+				equal( ui.item.value, "javascript", "Item gained focus" );
+				$( this ).text( customVal );
+				event.preventDefault();
+			}
+		});
+
+	element
+		.simulate( "focus" )
+		.autocomplete( "search", "ja" );
+
+	setTimeout(function() {
+		element.simulate( "keydown", { keyCode: $.ui.keyCode.DOWN } );
+		element.simulate( "keydown", { keyCode: $.ui.keyCode.DOWN } );
+		equal( element.text(), customVal );
+		start();
+	}, 50 );
+});
+
 asyncTest( "handle race condition", function() {
 	expect( 3 );
 	var count = 0,

ui/autocomplete.js

@@ -545,7 +545,11 @@ $.widget( "ui.autocomplete", {
 		}
 		if ( this.menu.isFirstItem() && /^previous/.test( direction ) ||
 				this.menu.isLastItem() && /^next/.test( direction ) ) {
+
+			if ( !this.isMultiLine ) {
 				this._value( this.term );
+			}
+
 			this.menu.blur();
 			return;
 		}