When the command dialogs from two ImageEditors on a page are opened consecutively, the second dock is rendered with wrong position. The issue most probably comes from the fact the second dock element (ToolsPanel) is appended to its parent ImageEditor, but not to the form.

Assuring that each dock is appended to the form element can be used as a temporary workaround of the issue:

        <telerik:RadImageEditor ID="RadImageEditor1" runat="server" Width="680" Height="450" OnClientDialogLoaded="ClientDialogLoaded"
            ImageUrl="waterpool.jpg">
        </telerik:RadImageEditor>
        <telerik:RadImageEditor ID="RadImageEditor2" runat="server" Width="680" Height="450" OnClientDialogLoaded="ClientDialogLoaded"
            ImageUrl="waterpool.jpg">
        </telerik:RadImageEditor>
        <script>
            function ClientDialogLoaded(imageEditor, args) {
                setTimeout(function () {
                    $telerik.$("#<%=form1.ClientID %>").append($get(imageEditor.get_id() + "_ToolsPanel"));
                }, 0);
            }
        </script>