1. Open the 3den editor
2. Place down a player, and a module to make this player zeus
3. Place down a marker fo the "empty" type, and give it some text
4. Play the mission, open the zeus interface, and look at where the marker should be on the map

Additionally:

5. In the zeus interface go to the markers tab, and search for "empty".
6. Place down a new marker fo this type and add text to it.

The marker and added text will be invisible.
Other than it being invisible you can still just move it around like any other marker.

This is not mentioned in the changelog and I see no reason for this, hence the assumption that it's a bug.