NullReferenceException - SF window is across two monitors

Had the SF window straddling two monitors, and clicked Play - all of the nodes in the SF window disappeared and the console began shooting out hundreds of nullrefs:

NullReferenceException: Object reference not set to an instance of an objectShaderForge.SF_PassSettings.OnLocalGUI (Int32 yOffset, Int32 in_maxWidth)
ShaderForge.SF_Editor.DrawPreviewPanel (Rect r)
ShaderForge.SF_Editor.OnGUI ()
System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:222)

Couldn't move or close the the SF window, had to restart Unity