I was using the Moodle QA for Moodle 2.8 and tried clicking the "Switch to base" button in the Theme Switcher block on the right sidebar. The first time I clicked it, it worked fine. However, when I tried to change back to the original theme that I had (by clicking the "Switch to clean" button), the page just refreshed. I refreshed the page and tried again, but that only worked some of the time. It seems like the theme doesn't change when there's a "theme=base" or "theme="clean" parameter in the URL.
The issue exists in the latest version of Chrome (stable, Chrome 35) and Firefox (Firefox 30.0) as of the creation of this issue. There's a little more on the issue in the "Steps to reproduce" below.
Steps to reproduce:
1. Go to the Moodle QA demo.
2. On the right sidebar in the Theme Switcher block, click the "Switch to base" button.
3. Now, on the homepage with the base theme, click the "Switch to clean" button. It should be in the same place as the "Switch to base" button.
4. Notice that the page refreshes, but the theme doesn't change. If you manually change the "theme=base" to "theme=clean" in the address bar, the theme will change as it should. If you do that and get back to the homepage with the clean theme and then click the "Switch to base" button again, you should notice that the theme once again doesn't change even though the page refreshed. Also, in the address bar, it should have a "theme=%20base" in it. As I said earlier, the issue seems to be that the theme doesn't change when there's already a "theme=base" or "theme=clean" parameter in the URL.
This might affect more than just Moodle 2.8, but I couldn't tell because I didn't see the Theme Switcher block on the Moodle 2.7 demo.