This SSIS package is made up of several tasks.
The second task fails (it's a SQL task, a permissions error - now fixed and reason for failure not important!). In the job history I can see that task failing.
The only precedent condition is a success condition on the next task. No further tasks run. The whole job reports success despite this task failure. Why?
(I do have an event in the OnError on the task that fails - which logs to a separate database - and this works.)