Simutrans: 120.2.2
Pakset: pak64.german 0.112.3.7 ( Makeobj version 55.1 for Simutrans 112.1 and higher )
If a groundobj is found on a field, the marker is not displayed.
Marker image is only shown if the tile is almost empty (with some exceptions: trees and powerlines).
It has been like this from the very beginning more than 10 years ago.