🚀 go-pugleaf

I'm doing a little Rexx programming and came upon the following:

--------------------------------------
/* */                               
                                    
line = "prpipgphptp"
                                    
do while((n = pos("p", line)) \= 0) 
 line = overlay(" ", line, n)       
end                                 
                                    
say line                            
                                    
line = "prpipgphptp"                
                                    
n = pos("p", line)                  
do while(n \= 0)                    
 line = overlay(" ", line, n)       
 n = pos("p", line)                 
end                                 
                                    
say line                            

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The output when this program is run is the following:

prpipgphptp
 r i g h t

My question is simple - is this a bug or a limitation of the 
Rexx programming language?  Or is it that I'm doing something
wrong?

						Jake