As a bit of explanation behind my assertion,the follwing command shows no changes (diff between the two branches and their common ancestor, AFAIK) git diff origin/stable...upstream/master
but this (diff between the heads) does
git diff origin/stable..upstream master
it turns out that reversing the order of the branches for the common ancestor diff also shows changes: git diff upstream/master...origin/stable
(note that in this case origin -> github, upstream -> fedorahosted)
Like I said, it looks like I have more learning to do on how to use some parts of git.
In your examples you use two fullstops and three fullstops. Be very careful about that, they have different meaning. Furthermore, they have different meaning in generic git commands from the meaning in git diff command (extremely confusing). It's probably a good topic for the next "git tip of the day".