What comes here are detailed instructions to reproduce a very, very subtle bug for doxygen-1.4.x. You should follow it to the point:

1.) Open the editor of your choice (or vi) and set tabstop=4.

2.) Create a header containing exactly the follwing lines:

namespace toxic {
/*!
 *  @code
 *      DoxyJam doxJam;
 *      @endcode
 */
class DoxyJam {};
}

2.) Goto line 3 and make sure that "*" is separated from "@" by two _spaces_.

3.) Goto line 5 and make sure that "*" is separated from "@" with a _tab_.

4.) Let doxygen work on this file.

You should get something like:
"test_header.h:10: File ended in the middle of a comment block! Perhaps a missing \endcode?"
and no documentation.

5.) Now goto line 3 again, remove the spaces and place a tab between "*" and "@".

6.) Run doxygen again. Voila, now it works.