Ok, now I think I get it. This is a fun one! How about adding them to a staic list when you assign the task and then if ownership changes and they are on that static list then trigger your exception reporting? Key here is to remove them from the list when the task is completed.
Hmmm, there are many tasks set up for everyone every day though, like every time a price page is visited for example. If they remain in the static list, wouldn't a notification still happen everytime ownership changes?
What would the set up look like? I can't locate the "if task ownership changes" for the adding to static list part