For what it's worth, I use Squeak 3.1a on both Mac and Windows fairly regularly, and I have seen this behavior on Windows, but never on the Mac. (although it only occasionally happens on Windows)  It would appear to be a Windows-only problem.

- Doug Way
  dway at riskmetrics.com


Mike Rutenberg wrote:
> 
> I have also seen this on the newest Win32 VM/Image.
>         VM: 3.1 alpha build 3
>         Image: 3.1alpha with updates 3910
> But you are right, the images are from earlier images and somewhat
> earlier VMs.
> 
> You are right that drag does it with only square outlines (as far as I
> know).  The picture
>         movingawindow.gif
> has actually already been moved, and what is showing is both the remains
> of the old window and the not properly displayed new window.  The
> outline of the new window has drawn properly though, with the rounded
> edges.
> 
> For a bit more content, I have attached an earlier message I had sent to
> Andreas.  He has apparently also sometimes seen it.  It seems that the
> bits are getting painted correctly into the Squeak internal Display, but
> then are not making it out to the Win32 screen (I say this because the
> Utilities grabScreenAndSaveOnDisk looked fine while the actual screen
> contnued to look garbled).
> 
> Mike
> 
> ______
> Date: Sun, 11 Feb 2001 20:10:14 +0300
> From: mdr at scn.org (mike rutenberg)
> Subject: Display update problem with new Windows VM
> To: "raab, andreas" <andreas.raab at disney.com>
> 
> Andreas,
> 
> There seems to be a problem using the 3.0 VM in updating the Win32
> window from the internal Squeak Display.
> 
> Attached is a screen snapshot illustrating the problem (Most of the
> window is unpainted).  I just started the image and had not done
> anything useful yet.  Configuration is:
>         VM Option: Defer Display Update is CHECKED
>         VM: Win98 3.0 alpha 3
>         Image 3.0 with updates to 3414
> (Picture is in badscreensm.gif)
> 
> Yesterday I had a similar problem with an earlier image and a slightly
> older VM
>         VM: Win98 3.0 alpha 1
>         Image: 2.9alpha to update 2774
> In this case the system had been running for a while and when I tried
> readjusting a window's configuration it did not repaint.  I used
> "Utilities grabScreenAndSaveOnDisk" to save part of the garbled region
> disk, and when I looked at the resulting GIF file it was perfectly fine.
> 
> It is not easy to reproduce, and it seems that it is only sometimes a
> problem (e.g. the 3.0 image from the picture is still running now and
> visually seems respond fine now).
> 
> Mike