Make sure that disconnected nodes aren't sorted/uniqued. Fixes #5791.

src/traversing.js

@@ -146,9 +146,9 @@ jQuery.fn.extend({
 				jQuery.makeArray( selector ),
 			all = jQuery.merge( this.get(), set );
 
-		return this.pushStack( set[0] && (set[0].setInterval || set[0].nodeType === 9 || (set[0].parentNode && set[0].parentNode.nodeType !== 11)) ?
-			jQuery.unique( all ) :
-			all );
+		return this.pushStack( isDisconnected( set[0] ) || isDisconnected( all[0] ) ?
+			all :
+			jQuery.unique( all ) );
 	},
 
 	andSelf: function() {
@@ -156,6 +156,12 @@ jQuery.fn.extend({
 	}
 });
 
+// A painfully simple check to see if an element is disconnected
+// from a document (should be improved, where feasible).
+function isDisconnected( node ) {
+	return !node || !node.parentNode || node.parentNode.nodeType === 11;
+}
+
 jQuery.each({
 	parent: function( elem ) {
 		var parent = elem.parentNode;

test/unit/core.js

@@ -501,6 +501,15 @@ test("add(String|Element|Array|undefined)", function() {
 	// use jQuery([]).add(form.elements) instead.
 	//equals( jQuery([]).add(jQuery("#form")[0].elements).length, jQuery(jQuery("#form")[0].elements).length, "Array in constructor must equals array in add()" );
 
+	var divs = jQuery("<div/>").add("#sndp");
+	ok( !divs[0].parentNode, "Make sure the first element is still the disconnected node." );
+
+	divs = jQuery("<div>test</div>").add("#sndp");
+	equals( divs[0].parentNode.nodeType, 11, "Make sure the first element is still the disconnected node." );
+
+	divs = jQuery("#sndp").add("<div/>");
+	ok( !divs[1].parentNode, "Make sure the first element is still the disconnected node." );
+
 	var tmp = jQuery("<div/>");
 
 	var x = jQuery([]).add(jQuery("<p id='x1'>xxx</p>").appendTo(tmp)).add(jQuery("<p id='x2'>xxx</p>").appendTo(tmp));
@@ -522,10 +531,6 @@ test("add(String|Element|Array|undefined)", function() {
 	var notDefined;
 	equals( jQuery([]).add(notDefined).length, 0, "Check that undefined adds nothing" );
 
-	// Added after #2811
-	equals( jQuery([]).add([window,document,document.body,document]).length, 3, "Pass an array" );
-	equals( jQuery(document).add(document).length, 1, "Check duplicated elements" );
-	equals( jQuery(window).add(window).length, 1, "Check duplicated elements using the window" );
 	ok( jQuery([]).add( document.getElementById('form') ).length >= 13, "Add a form (adds the elements)" );
 });