I ran the following in the no_passthrough suite.   import {configureFailPoint} from "jstests/libs/fail_point_util.js" ; import {ShardingTest} from "jstests/libs/shardingtest.js" ; const caseInsensitive = {     locale: "en_US" ,     strength: 2 }; // 2 shards. var st = new ShardingTest({shards: 2}); var testDB = st.s.getDB( "test" ); assert .commandWorked(     testDB.adminCommand({enableSharding: testDB.getName(), primaryShard: st.shard0.shardName})); // Create a collection with a case -insensitive default collation sharded on {a: 1}. var collCaseInsensitive = testDB.getCollection( "case_insensitive" ); collCaseInsensitive.drop(); assert .commandWorked(testDB.createCollection( "case_insensitive" , {collation: caseInsensitive})); assert .commandWorked(collCaseInsensitive.createIndex({a: 1}, {collation: {locale: "simple" }})); assert .commandWorked(testDB.adminCommand({     shardCollection: collCaseInsensitive.getFullName(),     key: {a: 1},     collation: {locale: "simple" } })); // Split the collection. // shard0: [chunk 1] { "a" : { "$minKey" : 1 } } -->> { "a" : 0 } // shard0: [chunk 2] { "a" : 0 } -->> { "a" : "b" } // shard1: [chunk 3] { "a" : "b" } -->> { "a" : { "$maxKey" : 1 }} // Note that we need two chunks on shard0 for this repro. My guess is that its because if we move // all the chunks from shard0 to shard1, we will somehow know to only target shard1 in the query // below. assert .commandWorked(     testDB.adminCommand({split: collCaseInsensitive.getFullName(), middle: {a: 0}})); assert .commandWorked(     testDB.adminCommand({split: collCaseInsensitive.getFullName(), middle: {a: "b" }})); assert .commandWorked(testDB.adminCommand(     {moveChunk: collCaseInsensitive.getFullName(), find: {a: -1}, to: st.shard0.shardName})); assert .commandWorked(testDB.adminCommand(     {moveChunk: collCaseInsensitive.getFullName(), find: {a: "a" }, to: st.shard0.shardName})); assert .commandWorked(testDB.adminCommand(     {moveChunk: collCaseInsensitive.getFullName(), find: {a: "c" }, to: st.shard1.shardName})); // Put data on shard0, that will go into chunk 1. const doc = {     _id: 0,     a: "a" }; assert .commandWorked(collCaseInsensitive.insert(doc)); // Perform a chunk migration of chunk 1 from shard0 to shard1, but do not clean up orphans on // shard0. let suspendRangeDeletionShard0 = configureFailPoint(st.shard0, 'suspendRangeDeletion' ); testDB.adminCommand(     {moveChunk: collCaseInsensitive.getFullName(), find: {a: "a" }, to: st.shard1.shardName}); // Equality predicate. Since the query has non-simple collation we will have to broadcast to all // shards (since the shard key is on a simple collation index). However, we return the result doc // twice which means we do not properly do shard filtering in this case . const results = collCaseInsensitive.find({a: "a" }).collation(caseInsensitive).toArray(); print( "results are " , tojson(results)); assert .eq(results, [doc, doc]);  // BAD! DUPLICATE RESULT! suspendRangeDeletionShard0.off(); st.stop();