This is true, but I've done DISM deployment on several Windows 8 UEFI PCs and this is the first time anything like this has happened.

Usually my deployment process involves my custom image that was installed in a VM with a generic installer key. I sysprep that image with an unattend.xml file but with no product key whatsoever slipstreamed in, and is set to start up at OOBE. Then, after the target hard drive is set up, I use DISM to deploy the custom image, boot the target PC to WinPE and apply boot files, restart it, and let it do its jazz. With Windows 8 PCs and 8.0, there wasn't any issues with activation and the embedded keys. Going to 8.1 required pulling the key and manually entering it in. I've done this many times now and it's gone screwy for the first time ever.