Following on from my - https://jamfnation.jamfsoftware.com/discussion.html?id=18390 question.
I can Netboot happily but the install won't block copy. The image is set to diskless. The drive is dismounted and quickly comes back. Casper images shows block copy, but this also quickly changed and fails back to file copy.
I did do a lsof and it shows files open on the Macintosh HD, but I'm not sure why. One for example was - efilogin.framework.
Best wishes
Michael