The existing post-install was not successfully patching the git-gui script, and thus was invoking the packaged osx app which uses the system tk, which is too old to work (and is no longer supported by Apple anyway).
The existing post-install was not successfully patching the git-gui script, and thus was invoking the packaged osx app which uses the system tk, which is too old to work (and is no longer supported by Apple anyway).