[Axial]

I have created a simple diagram that consists only of lines and rectangles. nothing else. However, I find it impossible to select and make longer only the black line in the diagram (see attachment - an OG doc zipped in order to be allowed to attach it) - it always affects (and screws up upon resizing) other objects that are center-aligned with it. It is not grouped, all connections are disallowed, and it just should not happen? What is going on?