There are two basic behavior changes here and bunch of testing to verify the new behaviors.
1) Previously purging a dataset would cause a creating job to be cancelled but all outputs would need to be "deleted" in order to cause the creating job to be cancelled. After this change the behavior is the same for both deletion and purging - the job will run until all outputs are deleted or purged.
2) Previously Galaxy jobs wouldn't attempt to cleanup purged datasets that were created by a running tool - this cleanup now occurs.
These are tackled as a pair because I assume the difference in the behaviors between deletion and purging was a hack around tools populating datasets that had been purged while running. Cancelling the job wasn't a sure fix - but it would reduce the likelihood of such problems. I think the new approach is a bit more robust and explicit.
Nicola Soranzo