Control Ward marked with red cross

Noob question:

I slowly start to understand the concept of wards, trinkets, control wards and lenses. I also understand that control wards can prevent wards from warding. Now I see these control wards on the map with a red cross across it. What does that mean? Does it mean that the ward is prevented from sight? But why does one ward control the other but not the other way around? First placed loses from last placed wards? I guess not..... Please advise. Thx in advance.