Steps to reproduce:

1. Create a new dashboard.
2. Create Action Log widget (with unchecked "Show header" checkbox) in the top-left corner of the dashboard (or any other place starting with the top row).
3. Save the dashboard and enter a kiosk mode.
4. Focus the widget by mouse. The page will slide down to allow the header to appear.
5. The vertical scrollbar will also appear causing unnecessary flickering.

Expected:
The scrollbar should appear when there is actually a scrollable content.