[ubuntu] Windows on 16.04 unity desktop suddenly looks "strange"

Recent installation of Ubuntu 16.04, unity.

For some reason the windows for some applications have started looking "strange"; I'm not sure how best to describe it, they look like the old Microsoft Windows 3.1 style windows and controls. I have attached a screenshot of an example (The music program audacious).

How do I fix this? I found nothing while searching, and I don't know enough about this kind of stuff to know what to do. Thanks.

Screenshot from 2016-05-03 23-40-01.png