[GENERAL] Search path in group_roles not honered for logins

CREATE ROLE db_users
  NOSUPERUSER INHERIT NOCREATEDB NOCREATEROLE; ALTER ROLE db_users SET search_path=mydb, public;

When I create a login,

CREATE ROLE oli LOGIN
  ENCRYPTED PASSWORD 'mXXX'
  NOSUPERUSER INHERIT NOCREATEDB NOCREATEROLE; ALTER ROLE oliver SET search_path=xmms; <---- I have to set this manually GRANT db_users TO ol;

Why is this such or is this an intended feature?

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TIP 9: In versions below 8.0, the planner will ignore your desire to
       choose an index scan if your joining column's datatypes do not
       match