bmake issue: ${VARNAME -- syntax error?

[Aleksey Cheusov <cheusov%tut.by@localhost>]

      0 ~> cat /home/cheusov/tmp/1.mk         
      all:
              echo ${SHELL
      0 ~> make -f /home/cheusov/tmp/1.mk all 
      echo 

      0 ~>

In the above code I expect a syntax error or at least a warning message about
unclosed {.  Is this a bug of bmake? Shall I send PR?

-- 
Best regards, Aleksey Cheusov.