It seems that previous differentials which had been accepted and landed (but not closed) were not auto-closed after reimporting the repository. The differential correctly links to a commit in the parent repository, but it seems that this alone was not enough to trigger the differential to be auto-closed.
Is this the expected behaviour? I feel as if the differential should be auto-closed in this scenario. Is there an easy way to reprocess a given repository and auto-close landed differentials?