Recently, a member of the patrizierforum has reproduced this behavior.
This happens when a treck is in a battle and you save and load the game. After loading the game the treck is free and drives on. The battleicon remains visible. If the treck reaches a destination town while the battle icon is visible the treck becomes a "ghost treck".
kalypso has some saves of that sort
for now:
dont save a game if a land/treck battle is going on!