Steps to reproduce:
1. Create a new project
2. Create a new scene through File -> New Scene
3. Create an empty object in Hierarchy window
4. Press CMD+S to open the save scene dialog and enter a scene name (don't click save yet)
5. Press CMD+Z to undo
6. Observe that the empty object in Hierarchy still exists (it was removed by undo, but the changes are not visible in hierarchy)
7. Press save in the save dialog window
8. Observe that the empty object in Hierarchy disappeared

Expected result: Editor windows should be repainted after undo actions while dialog windows are open so the user could see the changes OR undo should be disabled completely while dialog windows are open
Actual result: Undo actions while dialog windows are open do not repaint the editor windows and undone changes are only visible to the user after the dialog window is closed

Reproduced on: 2021.2.0a10, 2018.4.33f1

Reproducible on macOS
Not reproducible on Windows (undo commands are disabled while dialog windows are open)