[firebase_database] Difference in behaviour of onDisconnect().update(map) and update(map).

[siddhantkothari]

In Realtime Database, when we use some_reference.onDisconnect().update(map), the updates in the map happens one by one instead of all at once (like when we use some_reference.update(map)). Is this by design or a bug? If it is by design, how do I do it at once?