I've been following this up with the SDL forums, long suspecting that it is a bug in SDL2. There has been some talk about Direct3D renderers misbehaving with window resizing, and it may be that the bug we have is related to this one.
So I did an experiment to see whether selecting a different renderer would help. Sure enough if you set the SDL_RENDER_DRIVER environment variable to opengl then it seems to fix the problem.
Can anyone running Windows verify that IVAN full screen toggles without a crash when the sdl rendering environment variable is set in this way?