Anyone observing this behaviour?
Tested in both APEX 5.1.3 and 5.1.4 and both Chrome and IE11:
Date Picker field above Interactive Grid. When callendar is rolled out it is displayed below the IG header row - not allowing user to select any dates hidden under the header row.

The same also applies if Date Picker is shown inside the IG, this time it is displayed under the summary row of IG:

Is this a known issue? Can anyone think of a workaround?