Because the purpose of the test is to check the scenario when a new system comes back with the same address, while the SHUTDOWN message has been lost and the DeathWatch did not yet triggered -- before the fix this caused confusion with system message buffers since the new system was treated like it was the old one. Of course sequence numbers do not match up then.
So I set the deathwatch heartbeat pause to a "large enough" setting which is 60s in this test.