@alexandrephiev Talked to derrick about this a while ago this is not a bug but a missing feture what strapi is currently not planning to add since it would have lots of extra cost associated with it.
since lets say someting a content-type has 10k+ relations and now you change 1 relation should now all 10k relations get an event?
Also I would have to query the full content of every relation I run the event for.
How ever you could make this feture yourself if you realy wanted to and add like a relationChanged event to the eventhub