Thank you for the extra details. I was able to reproduce the flickering.
The page top toolbar is placed in RadWindow, which is a an absolutely positioned div element and a first child of the form.
RadWindow PageTop toolbar is configured (pinned) to be shown always on top of the visible page and to keep its top position when scrolling the page:
_positionOnPageTop: function ()
var wnd = this._toolbarHolder;
var screen = wnd._getViewportBounds();
var x = screen.scrollLeft; // + screen.x;
var y = screen.scrollTop; // + screen.y;
When the user scrolls down the top property value changes and the div is repositioned via the wnd.moveTo() method. The calculations require time and this is causing the browser flickering.
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