You for sure don't want it to be on "IDE master" as that would defeat the purpose of moving it. Try it on slave/secondary
Other than that you are going to need to ask the CentOS folks just how to do this. AFAIK it would be the exact same on metal. Just guessing because I don't do a lot with rpm based OSes the bootloader is seeing both bootable drives and is picking the wrong one. Probably because the distros are trying to dumb down these OSes and make everything automatic so the end user does not need to know anything.