If page has no scrollbar and if hintbox is higher than the screen, then hovering the element with this hintbox, all elements on page are moving right.
This may cause the hovered element to move out of mouse pointer, that cause hintbox to disappear.
As a result, by hovering such elements on certain spots makes the screen to flicker.
And if element is narrower than scrollbar, it may be hard to see the hintbox at all.
This can be repeated in Monitoring->Problems in Actions column.