Doxygen v1.6.3 introduces a regression in macro expansion; macros that were expanded as expected in v1.5.9 are no longer being expanded.

The following options are used:
MACRO_EXPANSION=YES
EXPAND_ONLY_PREDEF=NO

The two macros that fail to expand in the following example:
   MYCLASSNAME - #defined within the file that uses it, and #undef'd before EOF
   OPT_ARG(a) - #defined in a separate header and indirectly #included.

Doxygen v1.5.9 generates documentation for a class named "TestClass" with a member function "SomeFunc".

Doxygen v1.6.3 generates docs for a class named MYCLASSNAME without the member function, and the following error:

D:/XT178/VAPSXT_DIR/MacroTest/MacroTest.cpp: 8: Warning: no matching class member found for
  TestClass::SomeFunc(int arg1OPT_ARGint optional_arg)



----------------------------
FILE "MacroDefs.h"
----------------------------
#define OPTION 1

#if OPTION
#define OPT_ARG(arg) ,arg
#else
#define OPT_ARG(arg) 
#endif

----------------------------
FILE "MacroTest.h"
----------------------------
#include "MacroDefs.h"

#define MYCLASSNAME TestClass

/// @brief Test Class
class MYCLASSNAME {
public:
   SomeFunc( int arg1
     OPT_ARG(int optional_arg) );
};

#undef MYCLASSNAME

----------------------------
FILE "MacroTest.cpp"
----------------------------
#include "MacroTest.h"

#define MYCLASSNAME TestClass

/// @brief Some function.
MYCLASSNAME::SomeFunc( int arg1
               OPT_ARG(int arg2) )
{}

#undef MYCLASSNAME