Bulk Delete is a useful tool for deleting large numbers of records as an alternative to using Advanced Find and then clicking delete (which can only remove up to 250 records at a time).
System Job records are a good candidate for using Bulk Delete because the number of records is always increasing. However, suspended system jobs (such as workflows that are waiting) cannot be deleted using Bulk Delete. At least that was the case until Update Rollup 12 or 13.
Workflows disappearing
I investigated a problem where running workflows were disappearing at random. Workflows would start, perform actions and then disappear. There were no system job records for the affected running workflows.
Bulk delete job for suspended system jobs
I noticed a monthly recurring bulk deletion job (added by the client) that deletes systems jobs which are suspended and where the recurrence start does not contain data. I wondered if this was the reason why workflows were disappearing, but I thought suspended workflows can not be deleted by bulk delete? That is what the SDK says.
So I tested this on a system with UR11 and sure enough I received the message:
The selected system job could not be deleted. Only completed system jobs can be deleted.Bug in UR13 (or UR12) or deliberate change?
But the problem system had Update Rollup 13 installed so I repeated the test on that system and found that the bulk deletion job did delete suspended workflows.
So I wonder whether this is a bug or a deliberate change?