Noob question about Marching & Formation window

I'm kind of an explorator when softwares are concern. If something is there I want to know about it.

Just for fun I dropped a map from the image tab in the Marching & Formation window. Sweet. I set a grid. Everything is fine. But I can't take off the image.

I tried everything. I searched all the menus from the right click. I rebooted. I also tried to drop another image. That was a bad idea. Now I have two different image stacking together with no way to move one or the other.

The only layer showing up in the layers menu from the right click is the grid.

Is it a bug or a feature?

Is it intented this way or am I missing something?