Before you accuse the help files of lying, consider that you yourself may be at fault.
In this case, you may be clicking within the bounds of a previously placed ship. Zoom out a little, and click next to it.
I moved the X axis 200 kilometers from where I'd placed the first destroyer. If that's within the bounds of a Hecate, then something's seriously wrong.
Anyway, here's that screenshot.

When I click anywhere on the grid for any purpose (other than clicking directly on the Ulysses that starts off on the map) it automatically selects the ship I placed rather than doing whatever the click was supposed to do. Additionally, I've discovered that I may add waypoints in addition to a ship, but only if the waypoints are placed first; after a second ship is in place, I can't place any more.
Furthermore, I may add any number of fighters, but as soon as a capital ship is placed, no more ships can be added to the map. So apparently the problem is restricted only to capital ships.