<script>
    var $E = Telerik.Web.UI.Editor;
    var startOffsetAttr = '_startoffset';
    var endOffsetAttr = '_endoffset';
    var startIndex = '_startindex';
    var endIndex = '_endindex';

    $E.DomRangeMemento.prototype =
    {
        restoreToRange: function (r) {
            this.compensateOffsetInIE9();

            try {
                this.restoreStart(r);

                if (this.endOffset === false) { r.setEndBefore(this.endContainer); } else if (this.endOffset == 'outside') { r.setEnd(this.endContainer, Math.max(1, this.endContainer.childNodes.length - 1)); } else { r.setEnd(this.endContainer, this.endOffset); }


                this.restoreStart(r);

                if (this.collapsed) { r.collapse(); }

                r.select();
            } catch (ex) {
                // Handle errors when nodes are detached from DOM after mode switching
            }
        },

        restoreStart: function (range) {
            try {
                if (this.startOffset === false) { range.setStartBefore(this.startContainer); } else { range.setStart(this.startContainer, this.startOffset); }
            } catch (ex) {
                // Silently handle errors when start container is detached
            }
        },

        compensateOffsetInIE9: function () { // IE9 has the nasty bug of moving the range selection with one character to the right
            if (!$telerik.isIE9) { return; }

            if (this.beginsWithWhitespace(this.startContainer)) { this.startOffset++; }

            if (this.beginsWithWhitespace(this.endContainer)) { this.endOffset++; }
        },
        beginsWithWhitespace: function (node) {
            return utils.isTextNode(node) && /^\s/.test(node.nodeValue);
        }
    };

    $E.RangeHolder.prototype._setRangeEdge = function (range, marker, toStart) {
        var offsetKey = toStart ? startOffsetAttr : endOffsetAttr;
        var offsetFn = toStart ? 'setStart' : 'setEnd';
        var indexAttr = toStart ? startIndex : endIndex;
        var index = parseInt(marker.getAttribute(indexAttr), 10);
        var offset = parseInt(marker.getAttribute(offsetKey), 10);

        if (!isNaN(offset) && !isNaN(index)) {
            var node = marker.childNodes[index];
            // Validate that the node exists and is connected to the DOM
            if (node && node.nodeType && node.ownerDocument && node.ownerDocument.contains(node)) {
                range[offsetFn](node, offset);
            }
        }
    }
</script>

<telerik:RadEditor
    RenderMode="Lightweight"
    runat="server"
    ID="RadEditor1">
    <Content>
        <br />
        line 1<br />
        line 2<br />
        line 3<br />
    </Content>
</telerik:RadEditor>