From the All Pages page of the wiki on ExpressionEngine.com (the expressionengine.com site itself, not the software in general), choosing from the namespaces dropdown sends you to a URL in which the slash after the word “wiki” is missing.
I start out at this page:
http://expressionengine.com/wiki/Special:Titles
I choose “category” from the namespaces dropdown and it sends me to this page.
http://expressionengine.com/wikiSpecial:Titles/category/
It should send me to this page:
http://expressionengine.com/wiki/Special:Titles/category/
The error doesn’t appear to be browser specific. Btw, what is the appropriate place/method for reporting problems with ExpressionEngine.com itself (not the software)?
In any case, hope that helps.