To examine: 1. ssh ubuntu@54.77.0.143 (pw: #######) (this is standard AWS EC2 instance with Ubuntu Server 14.04 LTS and mongo 2.6.3 installed from official repositories) 2. run ./restart.sh located in /home/ubuntu 3. after cca 1 minute, the script should end, you can ignore its output 4. run mongo shell 5. 'use mongoProviderTest' 6. run this query: db.getCollection( '__clean_random_history' ).find({$query: {$or: [{$and: [{version: {$gt: 1}}, {before: {$gt: {}}}, { "before.a" : "hello" }]}, {$and: [{version: {$gt: 1}}, {after: {$gt: {}}}, { "after.a" : "hello" }]}], version: {$gt: 1}}, $orderby: {version: 1}}) Each document in the output should look like {"":1234} which is clearly wrong. Restart mongodb service to see the proper output. additional notes: it is probably not matter of this specific installation, it fails on several different machines running different flavors of linux this EC2 instance was created solely for demonstrating this bug, you are sudoer, feel free to play with it as you want the restart.sh script only runs more sophisticated code written in Dart language. You should probably be able to reproduce this bug also on other machines: copy the appropriate files, install Dart SDK and run it. Note that even though Dart and mongoDart (connector library) are involved, this bug clearly cannot be blamed on them; no client should have the possibility to get the DB to inconsistent state.