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Since Confluence 6.13 when a user is deleted the anonymization process is started automatically by Confluence. But the "user" field type in metadata seems not to get anonymized because there is no automatic reindex started. Therefore you will find spaces or pages with this user in the metadata can be found after deleting the user as long as the search index is not rebuilt.
Solution
If you delete a user and have a field type "user" active in a metadata set, please rebuild the index. Afterwards you will not find documents with the old user name any more.
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