Doxygen 'forgets' the documentation of defines under certain conditions.

Example:

1. Create a file test.h with this content:

        /// @defgroup Test
        /// @{

        /// macro BAR
        #ifndef BAR
           #define BAR  someFunction(x)
        #endif

        /// macro Foo
        #define FOO 42

        /// @}

        /// @page page1 
        /// Use @ref FOO

2. Create an default configuration file using:

      doxygen -g

3.  In Doxfile, set:

     INPUT = test.h

4. Run doxygen:

     doxygen

Doxygen complains:

  D:/test.h:17: Warning: unable to resolve reference to `FOO' for \ref command

In the generated documentation the both macro BAR and FOO are missing.

Note:
 - the problem does not occur for doxygen version 1.6.2.
 - the problem also occurs in the SVN version 1.6.3-20100324.
 - the problem disappears if the BAR macro gets slightly modified
   (remove the #ifdef, replace #ifndef BAR by #ifndef BAR2 or just
    change the macro definition to '#define BAR 123'