While reading new posts i frequently mark feeds with to many new items frequetly as read. i use the shortcut Shift+A. Just now NewsBlur startet deleting my feed-subscription every-time i press the shortcut. i realized it only after having already unsubscribed to 4-5 RSS-Feeds
Update: I used a third party client to double-check. It seems as the subscriptions are only deleted (invisible) from the Web-view . After syncing Newsblur with Readkit the Feeds and Folders are still there but not visible on the website anymore.