I don't know if there's a setting for this in Unity somewhere or if the Unity devs believe the functionality is working as intended but I cannot isolate using Ctrl-Z (interpreted by the editor as "undo") to being interpreted by the game when the editor is in play mode. Instead, hitting this key combination gets shared interpretation by both the game and the editor, which means things are being undone live. I understand that all the settings should revert to their pre-play-button status but if you have a prefab open with auto-save checked, this is not the case. Prefabs with auto-save on will recognize Ctrl-Z and undo changes. Considering I was using Ctrl-Z as something my game interprets, this means at many points in my development I may have inadvertently undone minor changes to prefabs without even realizing it. I consider this a major bug! I wonder what other commands are being read by the editor when the game alone should be interpreting key hits. Is this indeed a bug or am I missing an editor setting that is making this occur?