Mongosync will only drop each individual views upon dropDatabase without dropping the system.views itself. This is because dropping system.views requires very special privileges that aren’t included in any built-in roles. This leaves a corner case where if a database with views is dropped on the source, the destination may still show the dropped database after commit with an empty system.views in that database. We believe this shouldn’t have any impact on the correctness of user data/application.

Similarly, if users turn on profiling on the destination (which could generate <db>.system.profile), mongosync will not be able drop the <db>.system.profile collection on the destination even if the source database is dropped.