It is not possible to change the read status on multiple messages on shared folders with read-only ACLs

On shared folders received, both Shared and Public, with read-only ACL by selecting multiple messages, it is not possible to change the Seen / Unseen flag.
Changing flags on a single message works.

Steps to reproduce

• share a folder to user user1 with read-only ACL
• copy some e-mails in unseen status to this folder
• log in with user1 and open the shared folder
• select multiple messages
• right click -> Mark Seen

Expected behaviour

• the messages are all marked as Seen

Actual behaviour

• messages remain marked as Unseen and no actions are reported in the imap log.