I'm having this issue with my Toshiba laptop with an onboard Trident Cyber 9388 video card, which I suspect is the root cause. What is particularly odd to me though is that this is an issue regardless of the video driver used, including VGA, SVGA, and various Trident drivers. Maybe it just has a terrible VESA BIOS; I'm not sure.

Is anyone familiar with this being an issue with Windows 3.1 that can be fixed with an update? I have tried several different versions of the SVGA driver, as well as different versions of Windows 3.x including 3.1, 3.11, and 3.11FW; all of them exhibit varying degrees of garbled video when switching in and out of a DOS window.