Message content is empty

The message content of a comment in the discussion timeline is not displayed, but the event is created and displayed. The "expand/collapse message" arrows work but don't display any message. The issue can be observed in: https://www.xwiki.org/xwiki/bin/view/ChangeRequest/Data/Creating-a-subpage-for-a-Re-bd5f6026-0c12-4634-97b5-37a9739a6f86/. Also check the images in the attachments.

 
The "content" textarea is also empty in the object of type Discussion.Code.MessageClass:

https://www.xwiki.org/xwiki/bin/edit/ChangeRequest/Data/Creating-a-subpage-for-a-Re-bd5f6026-0c12-4634-97b5-37a9739a6f86/Discussions/Message/5aeb2cdb-3222-45c4-90f2-c10ea2d4103d?editor=object