That's uh, odd. Never done that for me. Try posting over at the support site.
http://www.vbdrupal.org
Elmuerte is kinda busy, but the quality of the support and released bug fixes are good.
You can get it to change to another one by deleteing the phptemplate theme folder of the theme you switched to. Tweaks to defaultangy can be done through adding css to a style.css file in the defaultangy folder.
HappyPike - I believe it does, you just have to make sure the correct paths are set. For example I have vbdrupal at alleria.com and the forums in a subdir.