I confirm that when the mouse moves, it flashes the header. It does not do it with the slider.
Printable View
I confirm that when the mouse moves, it flashes the header. It does not do it with the slider.
This is only my opinion. In IE11, the flicker behind is due the the number of shapes that are both Sticky & Stretchy.
I would overlay a further Sticky group of the pale blue, dark blue and black banding the width of the Page Background.
I think this might mask out the flickering.
Acorn
As soon as I put a second item in the header that is a sticky and a stretchy it begins flickering.
Acorn..that does seem to help. For now I'm going to remove the stretchy but I may use your trick thank you.