"When the filter detects a statement that would modify the database, it attaches a routing hint to all following statements. This routing hint guides the routing module to route the statement to the master server where data is guaranteed to be in an up-to-date state. "
Does not specify that it only happens in the session where the write happened.
I don't find any reference to session or connection.
In my opinion making it clear would avoid any kind of confusion for all MaxScale users.