Michael, thank you for such quick answer

I just moved them... that's all, nothing deleted, nothing changed. I selected everything, I moved everything... I know about the limitations that you describe but this is not what happened... I didn't try to move the 3d object, I moved everything.
The hole was not created with boolean commands. I just made a rectang and a circle and extruded both of them... So I guess it is "extrude" not "diff"