The preview's hint line was drawn only after the render had landed, so the pinned preview block grew by a line on the frame the render arrived (a worker thread, so any frame) and the page below it moved down. A click made in that frame hit the wrong place: the gate's tests_slideshow::playback_settings_drive_the_slideshow_and_bad_ones_are_refused clicked "Random order" and the checkbox never changed.
The hint is drawn while the preview is still rendering too. A new test holds the render back, then lets it land, and checks that the page and a control keep their places.
Nathaniel Ledford
c32d776a0e