Maybe this feature works as intended but it caught me by surprise. I wanted to add M57 even though it was already in my plan, I wanted to see which cats it was in. I had inadvertently selected Alcor prior to clicking + (Add new object to list). I did the search, selected a single entry for M57, clicked "add selected" then I got the "really delete 1 object" popup. Clicking yes replaced Alcor with the 2nd M57 object. Repeating the process but selecting no to "really delete 1 object" added M57 as a new object.
Was this how V1 used to work or did the + always do an add, never a replace?
I'm not necessarily saying this is bad but I think it needs some cleaning up and/or protection.
Some possible solutions that come to mind (FWIW I think I like the second one best):
The + always adds objects, a new button to edit an existing
A user selectable option that would popup a window asking if they want to add a new object or replace the selected object.
A more descriptive "really delete 1 object" message like maybe "are you sure you want to replace Alcor with M57"
Depending what you do the mouse over should change from "Add new object to list" to "Add new or replace object to list"

Fixed. Always adds.