This issue could be argued as being a feature request, or argued as being a bug. As a new user to Affinity Designer, I like to poke around and try things out. I've noticed that the buttons in the top toolbar always remain active and enabled, even when they don't do anything and shouldn't be enabled. Examples: 1) On my mac the "My Account" button is enabled, even though clicking on it does nothing, as well as the Affinity Designer > My Account menu item is disabled. Instead of clicking on the button, getting no response, and then thinking it was a bug, it would have been nice if the button had been disabled. Example 2) I create two rectangles with one overlapping the other... with one of the rectangles selected, click the "Back One" button and the selected rectangle moves back. Clicking the button again does nothing. At this point the rectangle already is the back-most object and can't move back any more, but (IMO) since the back button can't do anything at that point, it should be disabled, and this seems like a better UX to me.
Jeff