Ćwarmin already has gotten one of these "problematic" things that tend to pop up in my conlangs. I am not much for the painstaking meticulous diachronic derivation of a conlang - although it certainly would be good for consistency's sake.
First look at the case and definiteness systems. The combination is full of intentional gaps. That is all fine and dandy, but I later came up with the idea that the definiteness system is the result of a previous proximative-obviative system that has been re-analysed. Makes sense that far, doesn't it. But ... morphologically it doesn't seem to make much sense - I don't really see any way a proximative or obviative marker would fail to combine with certain cases the way they've done in Ćwarmin. Nor does there really seem to be all that much logic to where the failures occur.
Well, I imagine there may be some way of salvaging it - I am not going to abandon it nor change these details - it's just that I basically have to say that "the hypothesis that Ćwarmin previously has been proximative-obviative is somewhat iffy given the facts, and we must hypothesize that several of its relatives instead have developed typical proximative-obviative systems independently while Ćwarmin itself has failed to entirely line up with such a system, and instead either developed some non-canonical variety or something slightly different from it."
On the other hand, flaws like these are appealing in their own way - they're a part of the artwork much like the various imperfections in the piece of wood that has been shaped into a small statue might contribute to its beauty.