Lines dissapering when pasting a shape

When I copy and paste shapes made with the rectangle tool If I place two shapes together so that the lines in the middle are overlapping they disappear. This also happens when I press paste while two lines are overlapping it will delete the overlapping line. Even if the lines are separate layers the overlapping lines will still disappear merging the shapes. I am not sure if there is an option I can disable or if my only option is to simply make new shapes and merge the layers later.