This was uncovered with the work on
On NodeStore.merge() the TarMK uses SegmentNodeState#fastEquals to efficiently determine whether there is something to commit and whether the base state changed since the builder about to commit was acquired. For efficiency reasons fastEquals can return "false negatives". AFAIU migration of binaries depends on this implementation detail because without this optimisation migration fails. (SegmentToExternalMigrationTest and ExternalToExternalMigrationTest fail).