To date i have found 3 examples where an item i relisted had the listing policy switch to a different listing policy, without my knowledge. It was only by luck i discovered the first one and then looked and found 2 more.
In my case the policy was switched to a much more expensive policy i have saved for larger, heavier items. It is likely those 3 effected listings would never have sold with the much higher cost shipping policy now on them.
Worse, when i viewed what policy was being used for the 3 listings, IT SHOWED THE PROPER ONE WAS BEING USED, but what was actually being used and shown to buyers was the more expensive one.
The fix was simple, i just used 'edit shipping policy for this listing only' and put in the proper amount.
This has happened on ebay.com........not sure if the .ca site is doing it or not as i haven't relisted anything on there recently.