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It is important to select the correct meta field group. Depending on the meta field group, a meta data field may be used in different contexts. A prime example of this is the "Keywords" meta fields. There is a "Keywords" meta data field in the meta data field group Asset → Images → IPTC and another "Keywords" meta data field in the group Asset → Shared → All asset types.
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The "All asset types" meta data field is extremely dynamic compared to the IPTC one: This meta data field may be applied to any asset and any keywords may be added or removed from this meta data field by any users with write-access.