I had this happen with a CU recently, and I saw someone that had the same problem with SP1. You download and install some patch - a CU or service pack. The final step after installation is to run psconfig on each server in the farm. However, psconfig tells you that it can't proceed because one or more of the servers are missing a required patch. It shows the server name, the patch name, and it says "Missing/Required". The thing it says is missing though is the exact patch you just got done installing. Frustrating, yes?
Fortunately, Sam from the UK Premier Field Engineering team had a work-around that fixed it for me, so I'm sharing it here on his behalf in the hopes that it will help you. Try running the command Get-SPProduct –local on the server that says it's missing the required patch. Doing so forces a timer job to run that does some version fix up. This solved the problem for me; hope it helps you if you find yourself in this position.