I managed to find an ok workaround. I update the label and data model every onkeyup event, but I only rerender the toggle panel on the onblur event.
I guess a better workaround would be to make the onfocus event of the text field set the input marker at the end of the already existing text. I'll look into whether that is possible or not.
update just outputText in header but not the whole panel.
That worked great. Thanks a lot!