My wife pretty much goes to Super Wal-Mart and H-E-B (a Texas grocery chain) for our food and about everything else. Sometimes the Walgreens. Each one has had numerous times where a posted price wasn't honored at the register, and promises to fix it go unfulfilled (like they have a couple of data entry clerks hidden in some back room perhaps?) The worst part is getting a manager or going to the Customer Service counter and having it take way too long to get the problem corrected for the moment.
This is not a K-Mart specific problem.