Steps to reproduce:
1. Click on Posts > Categories
2. Click on Add New
3. Enter a category name
4. Click Add New Category button
5. Expected Result: Screen refreshes, category appears in the list on the right, system displays message: "category "category name" has been added - FAILED
Actual Result: Nothing happens
6. Refresh the page
7. Category appears in category list on the right
This original (closed) thread describes the problem exactly.
I am having the same issue with WordPress 3.2.1 I don't see this as resolved because in my case I was experiencing the problem even before I had activated any plugins.
In my mind this is a bug in WordPress core. Can anyone else offer insight?