(Non)Autoscrolling Windows

[kddlab!atr-la.atr.co.jp!myers@uunet.UU.NET (John K. Myers)]

I am working with windows in a Program Framework.
I try to position text under program control, by using
:set-cursorpos and then :string-out.
If the string runs outside of the window, it should be clipped off.

Currently I am using normal :DISPLAY windows in one application,
and normal :INTERACTOR windows in another application.
I clip the output using
  (send stream :set-cursorpos X-position 0 :pixel)   ;:character  apparently not supported.
  (dw:with-output-truncation (stream :horizontal T)
    (send stream :string-out string))
in one case, no clipping in the other case.

The windows do not have scroll bars, but they are real
dynamic windows just the same.
The problem I am seeing is that the windows apparently
scroll themselves at random times, after some output
is displayed.  In one case, output sent to the center of
the window gets scrolled up so that it is in the center of
the first line.  In the case with the horizontal clipping,
output gets scrolled completely off the screen.
I'd think this behavior might happen if output goes off
the screen, but in the first case the output is guaranteed
to be in the center of the screen, and the second case
uses clipping to ensure the same.
  Other messages I use include :clear-window and
:compute-motion.

Why is the machine doing this, and, more importantly,
how can I set the windows so that they don't autoscroll?

Thanks,
  John Myers~~