Mentions without an anchor in changed content don't trigger notifications

Steps to reproduce:

1. Create a page and save it.
2. Edit the page again and add a mention macro without anchor. You can create a mention macro in the WYSIWYG editor with the @ shortcut and then remove the anchor parameter in the source view before saving.
3. Check if the mentioned user got a notification.

Expected result:

There is a notification about the mention.

Actual result:

There isn't any notification.