If child record is added on parent record then userevent triggers on parent record. If child record is created independently then userevent triggers on child record. If child record is removed from parent record in view mode using "remove" hyperlink, then no trigger occurs.

And the third sentence drives me crazy all the time 🙂

third rules is really frustrating... remove doesn't DELETE child record. It just removes value from the parent field (set null) it becomes orphan .. I created script for scheduled deleting orphans records

Yep I also went with the “deleteOrphanedRecords” scheduled script