Just found a weird effect on a lage site I manage. I recently upgraded to 2.3.1 and have not implemented tags on the site, but users have started to tag articles.
The site, http://www.3ammagazine.com/3am/, is organised by categories, and each article is in only one category. However, we've discovered that if an article is tagged with the name of a category, it appears in this category too.
e.g. an article in the Interviews category (cat 2) is tagged (among other things) 'fiction'. However, when the latest Fiction category articles are called with
$myposts = get_posts('numberposts=3&category=5');
the article is called by $myposts here too.
Why is this happening, is it intended, and if so, why? I'm sure tags and categories are meant to be different systems.