Menu: Ignore mouse events triggered due to page scrolling

Fixes #9356
Closes gh-1806

tests/unit/selectmenu/core.js

@@ -251,13 +251,13 @@ $.each( [
 			wrappers = menu.find( "li.ui-menu-item .ui-menu-item-wrapper" );
 
 			button.trigger( "click" );
-			wrappers.first().simulate( "mouseover" ).trigger( "click" );
+			wrappers.first().simulate( "mouseover", { clientX: 2, clientY: 2 } ).trigger( "click" );
 			assert.equal( element[ 0 ].selectedIndex, 0, "First item is selected" );
 			button.simulate( "keydown", { keyCode: $.ui.keyCode.UP } );
 			assert.equal( element[ 0 ].selectedIndex, 0, "No looping beyond first item" );
 
 			button.trigger( "click" );
-			wrappers.last().simulate( "mouseover" ).trigger( "click" );
+			wrappers.last().simulate( "mouseover", { clientX: 3, clientY: 3 } ).trigger( "click" );
 			assert.equal( element[ 0 ].selectedIndex, wrappers.length - 1, "Last item is selected" );
 			button.simulate( "keydown", { keyCode: $.ui.keyCode.DOWN } );
 			assert.equal( element[ 0 ].selectedIndex, wrappers.length - 1, "No looping behind last item" );

tests/unit/selectmenu/events.js

@@ -89,9 +89,9 @@ QUnit.test( "focus", function( assert ) {
 		button.trigger( "click" );
 		links = menu.find( "li.ui-menu-item" );
 		optionIndex = 0;
-		links.eq( optionIndex ).simulate( "mouseover" );
+		links.eq( optionIndex ).simulate( "mouseover", { clientX: 2, clientY: 2 } );
 		optionIndex += 1;
-		links.eq( optionIndex ).simulate( "mouseover" );
+		links.eq( optionIndex ).simulate( "mouseover", { clientX: 3, clientY: 3 } );
 
 		// This tests for unwanted, additional focus event on close
 		that.element.selectmenu( "close" );

ui/widgets/menu.js

@@ -64,6 +64,7 @@ return $.widget( "ui.menu", {
 		// Flag used to prevent firing of the click handler
 		// as the event bubbles up through nested menus
 		this.mouseHandled = false;
+		this.lastMousePosition = { x: null, y: null };
 		this.element
 			.uniqueId()
 			.attr( {
@@ -161,6 +162,17 @@ return $.widget( "ui.menu", {
 			return;
 		}
 
+		// If the mouse didn't actually move, but the page was scrolled, ignore the event (#9356)
+		if ( event.clientX === this.lastMousePosition.x &&
+				event.clientY === this.lastMousePosition.y ) {
+			return;
+		}
+
+		this.lastMousePosition = {
+			x: event.clientX,
+			y: event.clientY
+		};
+
 		var actualTarget = $( event.target ).closest( ".ui-menu-item" ),
 			target = $( event.currentTarget );