My understanding is as with others here, where only the person who created a task can clear it -- I find this to be a security issue, since a malicious user could trigger a task, then clear the result so that it isn't in a log. The alternative is letting all the completed/failed jobs pile up which makes it a mess to look at and hard to parse through over time.
I would like to see this behaviour changed so that:
1. An administrative user can clear all tasks.
2. User accounts can be configured so that they cannot clear their tasks after completion.