Finishing a release with git flow partially completes but fails silently

The normal git-flow process when finishing a release is:

1. Merge release branch into master
2. Tag master with the release version
3. Merge release branch into develop
4. Delete release branch

When used through Sourcetree, git-flow is only completing steps 1 & 2. No error dialogs.

—

To reproduce: make a test project initialized with git-flow, add a couple of commits on develop, start a new release, make a commit in the release branch and try and finish the release. I end up sat on master, release branch still there and develop missing the commit from the release branch.

I installed git-flow using Homebrew and tried the same test from the command line with git-flow. It works fine.

So I switched Sourcetree to system git-flow and tried again. I do get an error dialog now, with this message:

flags:WARN getopt: illegal option – f

 -- /var/folders/h8/n_m5b8zs26bdcng40f1p2xp80000gn/T/SourceTreeTemp.1BO8Ra 1.3

flags:FATAL unable to parse provided options with getopt.