The WPF host kept the name prompt open and said the name was taken; the port
kept the resource string but dropped the message, and the New / Clone / Rename
/ Add-preconfigured handlers only return early on a collision. Nothing tells
the user why the list they just named did not appear, which reads as the dialog
having accepted the name.
The check belongs in the prompt, where the name is entered: OK stays disabled
while the name collides, so no flow can be handed one. Rename passes the name
of the list being renamed as allowed, because that is a no-op rather than a
collision with itself.
Assisted-by: Claude:claude-opus-5:Claude Code
Siegfried Pammer