The support staff resolved one problem (making links in Categories list in the sideboard work again) by inflicting another problem.
My blog is in Russian and to avoid long and gibberish post slugs I always use numbers as slugs. Now somebody changed that back to unintelligible long line. Fine.
But cross links in all of my posts to other posts in my blog no longer work, as the slugs are different. They changed slugs in posts, but not in links. And manually changing every cross link in hundreds of my posts is absolutely out of the question.
I've already written to Support Staff but this really bothers me a lot. Beware all Cyrillic users who had 404 problem solved by staff.