When I write JavaDoc-style comments in my code, Vim highlights the first sentence of them specifically:

Why does this happen? The problem occurs regardless of the colorscheme I use, so I’m assuming it has something to do with my java.vim file, but I’ve never modified it or anything.
Like jackrabbit said, the first sentence in a Javadoc comment is special. Vim highlights it for you so that you clearly see what will be used as the comment summary in the generated documentation. Still, if it bothers you, you can disable Javadoc highlighting by defining
java_ignore_javadocin your vimrc file.