Reproduced on demo : https://aspnet.daypilot.org/demo/Calendar/Crosshair.aspx
When option Crosshair=header is active, if you are in a cell, column and row headers are highlighted => OK.
From a cell, if you move mouse to the left horizontally on the row, arriving at the row header, the higlight disapear on both column and row headers => OK
From a cell, if you move mouse up the top vertically on the column, arriving at the column header, the higlight stay on the first row header and on the column header => ERROR
It cause us problems since we defined links action in the columns headers that are now masked by the crosshair highlight div (<div class="[theme]_crosshair_top" style="position: absolute; left: 0px; right: 0px; top: 0px; bottom: 0px; background-color: red !important;"></div>).
For information, bug was introduced by version 2019.2.3715 (working as expected in 2019.2.3711) and is still present at this day (v2020.1.3734).