MongoDB doesn't allow deletion on capped collection. When Mongorestore performs restore with oplog replay, it should ignore the delete operation on the capped collection. Otherwise, mongorestore will fail with the following error message:
Failed: restore error: error applying oplog: applyOps: (IllegalOperation) cannot remove from a capped collection: test.cappedColl
After discussion, we think the server should relax the restriction on applyOps for deletion since what mongorestore does with applyOps is very much like the initial sync during replication.