@mhayden, ok I see what you are meaning. Anytime we give a previously used computer to another user, we always erase the drive and re-image it using Casper Imaging. That way we know the new person has a freshly setup drive without any potential software issues. I'm not sure I'm going to be much help to you in the workflow you are using.
If you insist on not imaging using Casper Imaging or the imaging tool of your choice, you can alternatively boot into the Recovery Partition and use Disk Utility to erase the volume/partition and then use Internet Recovery to re-install the OS on that computer. You may need a valid Apple ID that has 'purchased' the OS which will get downloaded and installed. That OS is determined by the recovery partition if I'm not mistaken. In other words, if the computer came with 10.10 but has since been upgraded to 10.11 and therefore has a new 10.11 recovery partition, it won't let you use Internet Recovery to download/install 10.11 without a valid Apple ID that has purchased 10.11. Hope that makes sense. I don't personally recommend this method, but figured I'd throw it out there since you're not imaging these computers.
@mhayden if you have physical access to the computer, you could always login to the computer with the Casper management account and go to System Preferences and click on Users & Groups and delete the user account from there (with secure erase if you want) and create a new account for the new person. I just think you would have less to worry about if you re-image the computer.
I'm sure I would; however, at this time we so rarely need to reimage that the time spent building and maintaining images isn't worth it. Everyone's happy with a quick wipe, so we're not rocking the boat. We don't have any software we need to put on there that isn't already handled by policies or VPP.
So back to topic, even after wiping the device, re-enrolling using Pre-Stage Enrollment, it still says MDM = No. Is this a settings issue or should I call support?