performed the update from 1.4.01 to 1.6 and seemed that every went well. However, I now noticed that the page for category managemet has problems (see screenshot).
The html source is just a div element, i.e. no doctype definition, no html element and so on. Seems that the code returned by an AJAX request is displayed without integrating into the current page.
Click thumbnail to see full-size image