Due to a known limitation of distributed transaction, the concurrent_drops_and_creates.js test may cause sporadic failures when executed against a sharded cluster containing more than one shard, under the following circumstances:

1. DB1 gets created, with shard1 randomly picked as its primary shard
2. The unsplittable DB1.coll1 collection gets created
3. DB2 gets created, with shard2 randomly picked as its primary shard
4. a new transaction is opened
5. a new document is inserted into DB1.coll1; being the recipient of the first TXN write op, shard1 becomes the coordinator of the transaction
6. the unsplittable collection DB2.coll2 gets created on non-TXN coordinating shard2

The transaction commit fails with an unexpected OperationNotSupportedInTransaction due to step 6.