another Phab question: Local commits

Hi all, I wanted to make a comment in a Phab revision and refer to performance of a particular commit. So, I found the "Local commits" section of my page (https://phabricator.haskell.org/D73). But, those SHA's ("Commit" and "Tree") seem not to be related to others. The correct SHA, as I can see it, is the bit after "rGHC" in the "Description" field of "Diff 2". That SHA corresponds to the SHA I have on my own machine. What are the "Local commit" SHA's? Is there a way to refer to a particular commit in a Phab comment? And, while I'm at it, why do I have *2* Diffs here? I submitted only one git commit. One of the diffs (#2 a.k.a. #161 -- there seem to be two numbering schemes) is empty. Many thanks! Richard