After years of reading and trying to implement... This man just rocked it! Absolutely clear and consistent.

I think it is a reasonable idea to link any defect to the original story that it is a defect against. A defect, however, may be at many different levels of the functional decomposition. Some flexibility may be needed here.

I would argue that since Epic should mean "too big for a sprint" that is may or may not span a release. I suggest you think of "levels of work". On the problem side, what do you want to call something that can be done by one person is less than a day? I would suggest "task". For something that can take a few people one or more days but less than a sprint?: I would suggest "story". For something that takes one or more people and longer than a sprint? I would suggest "epic". So what about feature? I would use feature to describe a solution that takes one or more people to work on, typically longer than a sprint. Our issue, of course, is that people come to us with features, we have to work to figure out why they want that feature. Turn a solution into a problem to be solved. Releases are collections of stories, perhaps epics, and features that we expect will be delivered by a given date.