I have the following subroutine:
      SUBROUTINE fie(xx,xxb)
      IMPLICIT NONE

      INTEGER, PARAMETER :: A = 7
      INTEGER, PARAMETER :: B = 3
      DOUBLE PRECISION :: xx((A + 5) * B)
      DOUBLE PRECISION :: xxb(((A) + 5) * B)

      END

The result in Doxygen is:
subroutine fie  (DOUBLE PRECISION,dimension((a + 5)     xx,
                 DOUBLE PRECISION,dimension(((a)        xxb 
                ) 	

Instead of:
subroutine fie  (DOUBLE PRECISION,dimension((a + 5) * b) xx,
                 DOUBLE PRECISION,dimension(((a) + 5)    xxb	 
                )

replacing in fortranscanner.l the line:
ARGS      {BS}("("[^)]*")")
by:
NRB       [^()]*
RBWRD     "("{NRB}("("{NRB}")"|")")
WRD       {NRB}{RBWRD}
ARGS      {BS}"("{WRD}*{NRB}")"

the output is OK. I don't know if I have to change something in fortrancode.l as well?
This implementation is for a set of with a maximum of 2 levels of round brackets in the (a.o.) dimension statement. I have not been able to make a recursive version for it (I think 
RBWRD     "("{NRB}({RBWRD}|")")
might work), but I get the error message:
../lib/libdoxygen.a(doxygen.o):doxygen.cpp:(.text+0x20123): undefined reference
to `vtable for FortranLanguageScanner'