Update_sharded.js expects the mongos targeting behavior to conform to 4.2 behavior as seen in SERVER-34971. This test will fail in the sharding_last_stable_mongos_and_mixed_shards suite.

Note that this test is already blacklisted as of the writing of this ticket – but it's blacklisted under the wrong category. It should be changed to "unblacklist when 4.2 is last-stable" category.