Index: typo3/jsfunc.tbe_editor.js
===================================================================
--- typo3/jsfunc.tbe_editor.js	(revision 6468)
+++ typo3/jsfunc.tbe_editor.js	(working copy)
@@ -324,16 +324,21 @@
 		document[TBE_EDITOR.formname][theField].value = RTEcontent;
 		alert(document[TBE_EDITOR.formname][theField].value);
 	},
+	// strips the "table", the "field" and the "uid" from the fName
+	extractDataFromFieldName: function(fName) {
+		var idx   = 2 + TBE_EDITOR.prependFormFieldNamesCnt;
+		var table = TBE_EDITOR.split(fName, '[', idx);
+		var uid   = TBE_EDITOR.split(fName, '[', idx + 1);
+		var field = TBE_EDITOR.split(fName, '[', idx + 2);
+		return { table: table.substr(0, table.length-1), uid: uid.substr(0, uid.length-1), field: field.substr(0,field.length-1) };
+	},
+	getElementFromFieldName: function(fName) {
+		var data = TBE_EDITOR.extractDataFromFieldName(fName);
+		return TBE_EDITOR.getElement('data[' + data.table + '][' + data.uid + ']', data.field);
+	},
 	fieldChanged_fName: function(fName,el) {
-		var idx=2+TBE_EDITOR.prependFormFieldNamesCnt;
-		var table = TBE_EDITOR.split(fName, "[", idx);
-		var uid = TBE_EDITOR.split(fName, "[", idx+1);
-		var field = TBE_EDITOR.split(fName, "[", idx+2);
-
-		table = table.substr(0,table.length-1);
-		uid = uid.substr(0,uid.length-1);
-		field = field.substr(0,field.length-1);
-		TBE_EDITOR.fieldChanged(table,uid,field,el);
+		var data = TBE_EDITOR.extractDataFromFieldName(fName);
+		TBE_EDITOR.fieldChanged(data.table, data.uid, data.field, el);
 	},
 	fieldChanged: function(table,uid,field,el) {
 		var theField = TBE_EDITOR.prependFormFieldNames+'['+table+']['+uid+']['+field+']';
Index: t3lib/class.t3lib_tceforms.php
===================================================================
--- t3lib/class.t3lib_tceforms.php	(revision 6468)
+++ t3lib/class.t3lib_tceforms.php	(working copy)
@@ -5486,7 +5486,7 @@
 				browserWin.focus();
 			}
 			function setFormValueFromBrowseWin(fName,value,label,exclusiveValues)	{	//
-				var formObj = setFormValue_getFObj(fName)
+				var formObj = setFormValue_getFObj(fName);
 				if (formObj && value!="--div--")	{
 					fObj = formObj[fName+"_list"];
 					var len = fObj.length;
@@ -5495,7 +5495,9 @@
 						var m = new RegExp("(^|,)"+value+"($|,)");
 						if (exclusiveValues.match(m))	{
 								// the new value is exclusive
-							for (a=len-1;a>=0;a--)	fObj[a] = null;
+							for (a = len-1; a >= 0; a--) {
+								fObj[a] = null;
+							}
 							len = 0;
 						} else if (len == 1)	{
 							m = new RegExp("(^|,)"+fObj.options[0].value+"($|,)");
@@ -5508,14 +5510,23 @@
 					}
 						// Inserting element
 					var setOK = 1;
-					if (!formObj[fName+"_mul"] || formObj[fName+"_mul"].value==0)	{
+					if (!formObj[fName + "_mul"] || formObj[fName + "_mul"].value === 0) {
 						for (a=0;a<len;a++)	{
 							if (fObj.options[a].value==value)	{
 								setOK = 0;
 							}
 						}
 					}
+
 					if (setOK)	{
+							// remove the existing option element if there is only one element allowed
+						var el = TBE_EDITOR.getElementFromFieldName(fName);
+						var range = String(el.range).split(",");
+						if (range[1] == "1") {
+							setFormValueManipulate(fName, "Remove");
+							len = 0;
+						}
+						
 						fObj.length++;
 						fObj.options[len].value = value;
 						fObj.options[len].text = unescape(label);