HDRI cannot be disabled because it is a compiler option. I switched to HDRI because that will be enabled by default in ImageMagick 7.
As a work around you could choose to save your image as a png first and then convert this to a 12 bit tif. This seems to work (and save disk space) but is much slower.
As a work around you could choose to save your image as a png first and then convert this to a 12 bit tif. This seems to work (and save disk space) but is much slower.