When the sidebar tries to find out if a place has coordinates, it does so by checking if latitude and longitude are true. Since 0 evaluates to false, no coordinates are displayed for places on the equator or on the Greenwich meridian.
Similarly, the "add place" edit display evaluates the latitude (only). This works at the moment, but only by accident, because a zero coordinate is stored as "0.000000" in the edit data (
MBS-7438), which evaluates to true.