It's not constant, no, but I can only think of a very very small handful of words that break that rule. I mean, it wouldn't be English if a few words didn't have bizarre and totally arbitrary spellings, but there are very few common words that break the c rule. If you can point to a few that do, in English, (the only one that springs to mind is "soccer", and that's not the result of borrowing) that's great :)