using a defined constant to dimension an array

I'm confused about something I stumbled on this morning with array
definitions.  I want to pass an array to a procedure and I define the
procedure as follows:

Prototype--

D pushmode        pr              n                               
D entry                               like(mode) const            
D stack                               like(mode) dim(MAXMODE)     
D top                                 like(modetop)               
D 

Procedure interface--
P pushmode        b
D pushmode        pi              n                               
D entry                               like(mode) const            
D stack                               like(mode) dim(MAXMODE)     
D top                                 like(modetop)               
D                                                                 

MAXMODE is a constant defined before the procedure prototypes in the source
file.  It looks like this:

D MAXMODE         C                   const(50)         

The compile fails with various errors relating to the procedure definition
centering around the use of MAXMODE.  My favorite is: 

*RNF3764 30        027300  Definition of parameter (A(10)) not same as
definition of                                
                           parameter in prototype (A(10) DIM(50)).    


It looks like the compiler sees the named constant in the prototype, but not
in the actual procedure definition.  The program compiles fine if I
dimension the array in the procedure definition using a numeric literal. (I
didn't try using something other than 50, though.)  Is this the way it ought
to work?  Is a named constant less global than a variable, or does this have
to do with the behavior of the DIM keyword in a procedure definition versus
a D spec in a MAIN program?                                              
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