I have an ikiwiki, where I activated the plug-in sidebar: 
* enable sidebar? yes
* show sidebar page on all pages? yes

In order to create the page, I add a link to it on my entrance page: \[[sidebar]].
I now can choose where to put it, I put it as "sidebar", not index/sidebar. Language is Markdown, nothing else installed on the system.
After saving I can create the page clicking on the "?" and I fill it with links and the plugin pagestats.
The sidbar appears properly on all pages, also the tag-cloud.

However, when I try to go into "preferences" I just get an error message, saying it has the format html.
What is happening?