If the SourceTree app is located in a directory that contains spaces the git-flow features don't work. You get various error messages, e.g. when trying to start a new release.

In ~/.gitflow_export there's a path from SourceTree without double-quotes. I added them, but there's still various errors caused by "SourceTree.app/Contents/Resources/git_local/gitflow/gitflow-shFlags".

Moving SourceTree into another directory (like /Applications) works around this but I would have preferred to keep it in my user's directory (which has spaces).