I'd have to agree that this is what "should" happen. It is a pain to have to manually delete all the duplicate events. Problem, though, I think, is that writing up an algorithm for that is a bit problematic, particularly since a variation of a word in the description of the event can still result in 13 different christenings and multiple immigration events.
I should mention here: I put in a "Feature Request" about this: http://help.geni.com/entries/20667003-when-merging-profiles-also-me...