I discovered tonight that I'm having some very serious problems with categories:
- I can create new categories, but I can't assign posts to them. (It doesn't make a difference if I create the category in the Categories menu or directly from a post.) If I edit the post (either from the editing view or using QuickEdit), I can check the box for the new category, but as soon as I hit Update, the checkbox disappears and the Categories view shows 0 posts assigned to that category.
- I cannot delete any new categories I create. If I click delete in the Categories menu, the category flashes red and disappears, but if I refresh or click on something else and come back to the Categories view, the category is still there. It's also still in the terms table in the database. The only way to delete the category is to go into phpMyAdmin and drop that row.
I tried deactivating all plugins and switching to the default (unmodified Twenty Thirteen) theme to see if perhaps there was a theme or plugin conflict, but both above behaviors persisted. I also tried backing everything up and reinstalling WordPress from the Dashboard -> Updates menu, which had no effect.
I should mention that the data was imported from another WordPress installation. I believe something in the taxonomy tables has gotten messed up in the process. If I look at the database through phpMyAdmin, both the term_relationships and term_taxonomy tables have a red warning message saying, "No index defined."
I'm assuming that has something to do with my problem, but I'm not sure how to define the index in phpMyAdmin, nor do I know what it should be defined as.