Apparently categories were required in mantisbt 1.1.8 as well but not enforced.
Therefore I had a bunch of tickets using "empty" categories.

After having upgraded to mantisbt 1.2.x (following git branch at the time),
several issues presented themselves related to the empty categories.

For example, an issue could be changed, notes could be added, and so on, but the ticket could not be marked as resolved. Mantisbt 1.2.x complains that there is no category.

Furthermore, I left 'categories' empty for several projects when using 1.1.8.
Then with 1.2.x, an issue could not even be created without selecting a category (which was usually difficult since one did not exist although the category dropdown seemed to imply one was available (the previous blank one)).

Thus far I have worked around this by a) creating generic global categories
which all (most) projects inherit, b) removing/replacing the empty categories
(viewing the category table contents to find the projects containing the blank
categories, viewing the properties page of those projects, adjusting the
categories from there), and c) reassigning categories to the nonblank ones.

Was this just a fluke in my situation or something that the upgrade
procedure/script should address?