Not optimizing fixed-location accessor...

Does anyone know what this message means?

  Warning in (METHOD FOO::DISABLE-OUTPUT-CHUNKING
  (FOO::CHUNKED-STREAM-MIXIN)): Not optimizing fixed-location accessor
  STREAM::STREAM-BUFFER-STATE: no type information.

I'm getting it when I use WITH-STREAM-OUTPUT-BUFFER

  <http://www.lispworks.com/documentation/lw445/LWRM/html/lwref-549.htm>

and it looks to me as if it were just some compiler note about not
being able to generate the best possible code.  But maybe it's
something else?

Thanks,
Edi.