First of all, to reproduce the problem (I've been looking in all the wrong places first):
1. select a database
2. go to privileges tab
3. click edit privileges near a user
4. alter some privileges and click go.
5. the AJAX request is fired and the new privileges are saved, however the old privileges are still displayed in the overview table.
Please find a patch attached that fixes this issue. I did some basic testing and it works fine.