Discussion of a re-imported Wiki refers to the same forum of the original Wiki

How to reproduce

• Create a wiki and edit the index page
• On the index page, open a discussion, write something
• Copy wiki resource
• Open copy of wiki, open the index page
• Open the discussion tab
  => NOK: old discussion is visible
• Export wiki
• Reimport wiki
• Open reimported wiki, open the index page
• Open the discussion tab
  => NOK: old discussion is visible

If a user exports a Wiki learning resource and re-imports it into the same OO-instance, the the discussion tab of the new imported Wiki refers incorrectly to the forum of the old Wiki. All posts are visible at both Wiki discussions.

Expected behavior is the same as:
If a Wiki is copied within OO, then the new copy has a new fresh forum.