Post attachments are not shown if text is unchanged in post edit

[sebix]

• Create a post
• Add an attachment to a post, don't change the text
• save
  The attachment is not show

Issue has been reported several times, including:
https://forum.ubuntuusers.de/topic/anhang-wird-nicht-angezeigt/
https://forum.ubuntuusers.de/topic/anhang-wird-nicht-angezeigt-2