Fixed #1999 by replacing the 'no-cache' parameter if it is there instead of just appending.

src/ajax.js

@@ -197,8 +197,13 @@ jQuery.extend({
 		if ( s.dataType == "script" && s.cache == null )
 			s.cache = false;
 
-		if ( s.cache === false && s.type.toLowerCase() == "get" )
-			s.url += (s.url.match(/\?/) ? "&" : "?") + "_=" + (new Date()).getTime();
+		if ( s.cache === false && s.type.toLowerCase() == "get" ) {
+			var ts = (new Date()).getTime();
+			// try replacing _= if it is there
+			var ret = s.url.replace(/(\?|&)_=.*(&|$)/, "$1_=" + ts + "$2");
+			// if nothing was replaced, add timestamp to the end
+			s.url = ret + ((ret == s.url) ? (s.url.match(/\?/) ? "&" : "?") + "_=" + ts : "");
+		}
 
 		// If data is available, append data to url for get requests
 		if ( s.data && s.type.toLowerCase() == "get" ) {

test/unit/ajax.js

@@ -236,6 +236,36 @@ test("pass-through request object", function() {
 	ok( $.ajax({url: url(target), success: success}), "generic" );
 });
 
+test("ajax cache", function () {
+	expect(18);
+	stop();
+	
+	var count = 0;
+
+	$("#firstp").bind("ajaxSuccess", function (e, xml, s) {
+		var re = /_=(.*?)(&|$)/g;
+    var oldOne = null;
+		for (var i = 0; i < 6; i++) {
+      var ret = re.exec(s.url);
+			if (!ret) {
+				break;
+			}
+      oldOne = ret[1];
+		}
+		equals(i, 1, "Test to make sure only one 'no-cache' parameter is there");
+		ok(oldOne != "tobereplaced555", "Test to be sure parameter (if it was there) was replaced");
+		if(++count == 6)
+			start();
+	});
+
+	ok( $.ajax({url: "data/text.php", cache:false}), "test with no parameters" );
+	ok( $.ajax({url: "data/text.php?pizza=true", cache:false}), "test with 1 parameter" );
+	ok( $.ajax({url: "data/text.php?_=tobereplaced555", cache:false}), "test with _= parameter" );
+	ok( $.ajax({url: "data/text.php?pizza=true&_=tobereplaced555", cache:false}), "test with 1 parameter plus _= one" );
+	ok( $.ajax({url: "data/text.php?_=tobereplaced555&tv=false", cache:false}), "test with 1 parameter plus _= one before it" );
+	ok( $.ajax({url: "data/text.php?name=David&_=tobereplaced555&washere=true", cache:false}), "test with 2 parameters surrounding _= one" );
+});
+
 test("global ajaxSettings", function() {
 	expect(3);