When I run git rebase -i, it automatically uses the text editor, and now because I primarily use sublime it loads sublime.
However, unlike Textmate or vim, git rebase -i does not seem to know when Sublime has closed the file, so continues without waiting for Sublime to finish editing.
You can easily test this by running
EDITOR=vim git rebase -i HEAD~5
EDITOR=mate git rebase -i HEAD~5
EDITOR=subl git rebase -i HEAD~5
As you will see, with Sublime it does not work.