Format for %d includes unwanted preceding space

The log --format="%d" includes preceding space:

$ git log -n1 --format="XX%dXX" HEAD
XX (HEAD -> master)XX

I know of no other %<token> that is output in this way.

Is there a way of removing this preceding space through the format 
string, or will it need to be a code change?

-- 
Tom Hale