Unreplicated capped collections do not serialize writes (see SERVER-21646), which means that tailable cursors can miss writes that commit in a different order than they were inserted.

This problem has essentially existed since we implemented document-level locking in 3.0.

Instead of also serializing writes to capped local collections, which would affect performance of inserts into the system.profile collection, I propose that we ban the usage of tailable cursors on unreplicated capped collections since they never worked correctly anyways.