I previously created and saved a ship design with the name "Custom Cruiser 17".  The first screen snapshot shows that I have selected that ship design and the popup that appears when I hover over the button with the "+" on it.  When I click on that button, I am get the window shown in the second screen snapshot below.  As you can see, there are 2 buttons at the bottom: one says "Edit Existing Design" and the other says "Start New Design".  Since I wanted to edit my "Custom Cruiser 17" design I clicked on the "Edit Existing Design" button.  When I did, I was taken back to the screen shown in the first screen snapshot below.  I can repeatedly click on the "+" button and the the "Edit Existing Design" button and just keep cycling back and forth between the 2 windows.  This does not seem to be working the way it should be.  In order to actually edit the ship design, you need to click on the "Start New Design" button which then takes you to the screen where you can edit the ship design (third screen snapshot below).  When you go to save the design it offers the original ship design name by default, which lets you overwrite the original ship design with the new ship design, or you can provide a new name, which lets you keep the original ship design and get the new ship design.

If this is the way it works, why do you even need the window shown in the second screen snapshot below?  Why don't you just take the player to the ship design editing screen when they click on the "+" button?  What value does the second screen provide that I am missing?