wtFF?

git status
# On branch master
nothing to commit (working directory clean)
mray@morbo[11:19](master)[] ~/Opscode/pbi-tse/pbis/Conferences
$ git push origin master
To git@github.com:mattray/pbi-tse.git
 ! [rejected]        master -> master (non-fast-forward)
error: failed to push some refs to 'git@github.com:mattray/pbi-tse.git'
To prevent you from losing history, non-fast-forward updates were rejected
Merge the remote changes (e.g. 'git pull') before pushing again.  See the
'Note about fast-forwards' section of 'git push --help' for details.