Interesting... I don't have an answer, unfortunately, but I have used Flashrom successfully on the HDAMA in the past.
Can you try checking out a very old version of Flashrom, like from back when it was in coreboot-v2/util/? I'm thinking wayyyyy back, like at around svn revision 2000 in the 2005-2006 timeframe. Maybe there was some regression that never got caught.