Last modified: 2013-02-14 22:14:29 UTC
As outlined in this feature requirement: https://www.mediawiki.org/wiki/Echo_(Notifications)/Feature_requirements#Dismiss This means that both web and email notification checkboxes should be disabled for a dismissed notification type in the user preferences, which is not yet the case.
Fixed in https://gerrit.wikimedia.org/r/#/c/49174/