Can you let me know what template you're using? We test extensively with the built-in default Joomla admin template, Isis. If you're using a different one, it's possible there's a conflict. Let us know which one it is, and we can try to test.
In the meantime, I'd recommend switching to Isis and see if the problem goes away. That will help narrow things down, and let you configure things, temporarily.
Thanks,
Alex