@mentions in ListItemComments won't work for libraries

Category

[ ] Enhancement

[x] Bug

[ ] Question

Version

Please specify what version of the library you are using: [3.9.0]

Expected / Desired Behavior / Question

@-mentioning should work for lists and libraries.

Observed Behavior

When @-mentioning a user in a ListItemComments control connected to a list after saving a comment the @-mentions will be resolved to user names and emails will be send to notify the users. If the ListItemComments control is connected to a library the @-mentions will only appear while writing the comment. After saving the comment they appear as @mention{0} (1, 2, etc.) and no email gets send to the mentioned users.

Steps to Reproduce

Create two ListItemComments controls, for one set the listId property to the id of a list and for the other set the listId property to the id of a library.
Write comments mentioning yourself.