This document is intended to collect Matrix sync information which are documented or not in the official Matrix Spec. Especially, how raiden treats the syncing process introduces some special behavior.
Generally spoken the first sync delivers different results if a user already used this ID in Matrix or not. If already used the UserID is already part of the broadcast rooms (discovery, PFS, Monitoring). The Matrix Server will notice this and already send you information of the rooms you joined.
Events user receives: