createIndexes now disallows creation of indexes named '*' (literally a single asterisk). dropIndexes will not allow deletion of such indexes either, except by dropping a collection or all indexes for a collection.
Prior to the changes from 6fd95f8 as part of
SERVER-28200, the oplog entry for the "dropIndexes" command represented the index using its key pattern rather than its name. Dropping an index named "*" is interpreted by the replication subsystem as dropping all indexes and can cause the primary and secondaries not to have the same set of indexes.