Same offscreen window probe, production Native.MaintainTopmost:
19.7: non-overlapping window: mask position messages=1
19.8: non-overlapping window: mask position messages=0
19.7: owned settings popup (5 checks): mask position messages=5, settings position messages=5
19.8: owned settings popup (5 checks): mask position messages=0, settings position messages=0
Counts are WM_WINDOWPOSCHANGING messages on test windows, not optical flicker measurements.
