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Some times I notice I have a new badge by the number in the header, but there is no notification 'You've earned X badge, see it in your profile'. Over time I got the impression, that this happens only for badges I already have on SO (for example I've earned Citizen Patrol, but there was no notification for this; but when I earned Nice answer there was clear notification for it, since I didn't earn this at SO). Is it the case, or something wrong with me? If it's the case, why?