EDIT

The resolution is migrated correctly to the redmine custom field Resolution but the Status always is closed, see for example #5776

The mapping is defined correctly in the rake script migrate_from_trac.rake

RESOLUTION_STATUS_MAPPING = {
          # trac resolution name => redmine status or status name (names will be replaced by the actual status)
          'fixed' => closed_status,
          'invalid' => rejected_status,
          'wontfix' => rejected_status,
          'worksforme' => 'Worksforme',
          'duplicate' => 'Duplicate'
      }

The fix of this problem might involve fixing the status change in the last issue_journal records of the affected issues and also setting the final status of the issue.
This should most probably be done in the database directly. Needs testing before!