Occasionally the coverage popup for a branch job displays its popup partially off screen

Steps to reproduce

go to https://ci.jenkins.io/job/Core/job/jenkins/

mouse over the coverage for the `master` branch and wait for the popup.

Expected Result

The resulting popup is always rendered complete on screen or is within the scrollable page area

Actual Result

occasionally (depending on window size?) some of the popup is displayed outside the visible/scrollable region.