Replacing a mention placeholder when a new one is inserted does not work when using display-name-based mentions

When the caret is moved over an existing mention placeholder in the annotation textarea, if a new suggestion is selected, it is supposed to replace the mention "under the caret" with the newly selected one.

This works as expected with username-based mentions, but it doesn't work with display-name mentions.

Username-based:

https://github.com/user-attachments/assets/7d2699e8-2460-4636-8a53-ee0d3cb664c7

Display-name-based:

https://github.com/user-attachments/assets/feb64989-2226-4973-8bd1-256a8ed186fc