piping surprise

[Ray Andrews <rayandrews@xxxxxxxxxxx>]

    Speaking of female logic, I stumbled upon
      this:
      
      function bbb ()
      {
          vvar=4
          print -l "\nShall\nI\ncompare thee\nto a\nsummer's day?"
      }    
      
      function aaa ()
      {
          local vvar=1
          bbb
          echo "\nvvar is $vvar"
          vvar=2
          echo "\n=============\n"
          bbb | grep 'a'
          echo "\nvvar is $vvar"
      }
      
      %  aaa
      
      Shall
      I
      compare thee
      to a
      summer's day?
      
      vvar is 4
      
      =============
      
      Shall
      compare thee
      to a
      summer's day?
      
      vvar is 2
      
      ------------------------------------------------------------------
      
      By what thinking does the piping of a function's output thru grep
      cancel the assignment to the variable?  Do we really want that?