When the HTML content is set with nested list elements and an empty paragraph right after the primary list, deleting this empty paragraph will cause the nested list to go outside the list item.

This matter causes an incorrect HTML markup and additionally causes incorrect tool behavior.

Passing trough Design to HTML cures the issue (invoking the content filters) cures the issue, although there are cases where users cannot be prompted to do that.

Using native events to resolve the backspace behavior:

<telerik:RadEditor ID="RadEditor1" runat="server" OnClientLoad="OnClientLoad">
</telerik:RadEditor>

<script type="text/javascript">
    function OnClientLoad(editor, args) {
        editor.attachEventHandler("onkeydown", function (e) {
            if (e.keyCode == 8 && $telerik.isIE10Mode && !$telerik.isIE10) {
                var selElm = editor.getSelectedElement();
                var isCursorInFront = editor.getSelection().getRange().startOffset == 0;
                if (selElm && selElm.nodeName == "P" && isCursorInFront) {
                    editor.attachEventHandler("onkeyup", fixContent);
                }
            }
        });

        var fixContent = function () {
            editor.set_html(editor.get_html(true));
            editor.detachEventHandler("onkeyup", fixContent);
        }
    }
</script>