On opening an article for edit via the "edit" tag, a checkbox and the top category show up beneath the edit window. I cannot expand the category tree to check other categories.
Only sometimes, when I return to the edit mode on another way (like from the browser history), but even then not always, it may work as expected and I see the whole tree with a checkbox in front of each item.
The bug was in a 1.27 installation and is still present under 1.30 to which I copied the installation. [http://vexilli.net/w/ My wiki, for reference.]
Hoping for a fix, yours