This isn't quite a piece of 'lore', but it's a common enough thing in conlang descriptions. I will also have to mention some notable, very thorough exceptions.
Conlangers, even fairly far into developing a language, sometimes are happy just to list the cases, tenses, etc, without ever really describing their use. This betrays, in my opinion, a very naive (or essentialist, or whatever) view of what such things - cases, tenses, aspects, etc - are. This post will focus on cases, because they illustrate the problem fairly well.
One point I like to drive home is that names like 'accusative' are but labels, and the accusative of one language does probably not behave like the accusative of another. (For a scholarly source, see this.) They are not the same case except by virtue of having the same name. Yes, the prototypical use may be the same, but the prototypical use may be but one of the many uses of a case, and might not even be the primary use in practice – see, for instance, the plural genitive in Russian.
The naivety that I accuse this of showcasing is simply the notion that labels for grammatical things are somehow rigid references: all datives are the same, all accusatives are the same, all past tenses are the same, etc. This is far from the case. The dative of German, and the dative of Icelandic, to pick two very closely related datives are distinct cases. Despite sharing a name and even a historical origin, they are not the same case; yes, they share some properties - including some of their most frequent uses, but they also have several differences. For one, they don't go with the same prepositions (and of course, what I am saying about cases also applies to prepositions - 'in' in different languages differ!). Secondarily, they appear as quirky case subjects or objects with different verbs. Thirdly, being a quirky case subject (or object) is not quite the same thing in Icelandic as it is in German.
Looking at other languages with a dative, we find even more of a divergence between them. We also find that things sometimes go by different names but would fit very well in that category - e.g. the Finnish allative. As a sort of mid-conclusion: names can be both one-to-many and many-to-one, i.e. many things can carry the same names yet be quite different things, and many similar things can have different names.
As for non-case things, even pretty obvious categories like grammatical number may present a similar trap: the singular vs plural distinction is not the same in all languages – a trivial example would be things in general. Some languages prefer generic nouns to be singular, some prefer them to be plural, some seem to accept both ways by different ways of delineating them (e.g. lexically determined vs. influenced by grammatical context vs. other things.)
Tenses, moods and aspects, obviously, can present even greater differences.
To get back on cases, I would like to point to some good descriptions of case systems or even just locative systems that I feel avoid falling in the trap of 'just being a list''. Examples include Salmoneus' description of the locative adpositions of his Rawang Ata. Yes, this isn't about a case system per se, but functionally equivalent so you better just tolerate my use of it as an example.
A good example of doing a rather no-frills case system right is Carsten Becker's Ayeri. Some of the interesting stuff there appears in the interaction of case, transitivity and pragmatic concerns.
And a very naturalistic, alt-historiy Slavic case system is presented by Martin Posthumus in his Novegradian.
Of course, I am vain enough to toot my own horn here: I think there's some merit to my descriptions of my conlangs' case systems as well. The Bryatesle case usage description is fairly in-depth, but even then somewhat incomplete (see I, II, III, IV, V, and VI). Dairwueh has a short, but sweet description that attempts to analyze the cases in terms of abstract features. Ŋʒädär too has a nice description in the same style.
Sargalk and Cwarmin still have not gotten that treatment, but it'll happen soon enough.