Some case activities record the seconds, but some don't, leading to mismatched sorting in the case activities grid

Create a new case. The open case activity gets stored in the database with the seconds time component, e.g. 20:55:14
Add a followup activity. The seconds component for this activity is stored as "00", e.g. 20:55:00

If those two activities have the same minute component, the followup appears in the grid earlier than the open case, which makes no sense.

A similar thing can happen with email copies which store the seconds component.