What I did:
In a project or in the “On the Agenda” section, click the plus sign to create a new note. Tell Agenda to add the new note to some project project. The new note is named “Untitled Note”. Do not change the title. Click an all-day event in the calendar. In the pop-up select “Link to Selected Note” (i.e., the “Untitled Note” note).
Agenda briefly renames “Untitled Note” to the title of the all-day event and then immediately flips the name back to “Untitled Note”. If the sequence above is done with an event that is not an all-day event, when “Link to Selected Note” is clicked, Agenda renames “Untitled Note” to the name of the event and leaves the name that way.
What I expected:
With an all-day event, when “Link to Selected Note” is clicked, the note is renamed and left that way.
Things that might be helpful to know (Agenda version, OS and model, etc):
10.14.6 / 6.0.1 (85)
This is definitely an edge case, and not something anyone would do normally. Clicking the all-day event and choosing “New Note Linked to Event” is the normal method, and works fine. I just happened to follow the sequence above and noticed this minor anomaly.