Note: This makes assumptions on what the TODO comment in Synapse means: e26e6b3230/synapse/handlers/pagination.py (L262)
Due to lack of implementation, it is assumed that using the same filter across multiple calls to /sync OR /messages will result in the redundant members being excluded in the next request. For example, calling /sync, then /messages which returns some members, then /sync again will exclude the members due to them being in /messages.
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