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Since Confluence version 6.7.0 the Metadataset can no longer be added when creating a new page.
But it work's works for the all Confluence version versions lower than 6.7.0.
Solution
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The problem is solved for the mode modes "On" and "Limited".
Work around
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- Create a new page and save it
- Editing Edit the page and add the Metadataset
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