There are a number of pages using awkward work-arounds to refer to the C++ programming language in their titles (cplusplus, cxx, etc.). This version of MediaWiki does not (by default) allow the "+" character in page titles; later versions do. Please reconfigure to allow the "+" as described in 
Check out the last line of code in GuessRandom... the htmlification is messed up, it seems.
-- Yes, it's apparently a bug in the syntax highlighter. See TestMarkupBreakage
A minor, yet annoying bug in print.css: background-color property for pre is missing a semicolon