This made me try to pronounce those words with a ”k” and my first reaction was that I’d pronounce them differently when written with a ”k” than with a ”ck”. It might be that the ”ck” afdects the wovel before it. It seems similar like an ”e” can change the pronunciation of letters before it. (For example, ”mag” and ”mage”.)
I’m not a linguist, and not a native English speaker, so I’m not sure what to make of that.