Saxon

I am struggling to understand the result Saxon 9.6.0.3 EE gives me when I use a pattern @chapter/descendant::foo[1]@ with the descendant axis. Sample stylesheet is

sample input is

  
     
     1
     2
     
  
  
     a
  
  
     d1
      
       d2
      
  
  
     
      X
     
  

the result I get is

   1


   a


   d1


   d2

while I would expect to get

   1


   a


   d1

When I try to use descendant with pull style processing, as in the file

then I get the wanted result. I don't understand why the pattern based use gives a different result, is that a bug in Saxon or is my understanding of the use of the descendant axis in a pattern like @match="chapter/descendant::foo[1]"@ flawed?