The 'insertContent' method insert the content to the current position of the editor. So the editor must get focus before calling this method.
I supposed that and tried this immediately after texteditor has been inizialized:
$('#myid').texteditor('getEditor').focus().select();
$('#myid').texteditor('insertContent',myTxtStr);
but nothing.
I've to manually click with mouse on any position of texteditor and only after that 'insertContent' it'is ok