Looks like the mongo shell calls drop until a check that db.coll.count() == 0, but that check is succeeding when in fact the count is 1. I have only been able to reproduce this bug on RHEL 7.2 on Z. It seems like the connection made by mongoimport is still active (and not all its ops are finished) after the mongo shell received its status code and and even after the database is dropped by the shell. The leftover insert op from mongoimport seems to be happening after the drop and the db.coll.count().