git mktree error on Windows

[501st-alpha1]

I tried creating a new issue with git issues new "Some issue", and I got this error:

Traceback (most recent call last):
  File "[snip]\git-issues\git-issues", line 1243, in <module>
    issueSet.save_state()
  File "[snip]\git-issues\git-issues", line 438, in save_state
    self.shelf.sync()
  File "[snip]\git-issues\gitshelve.py", line 375, in sync
    self.commit()
  File "[snip]\git-issues\gitshelve.py", line 366, in commit
    tree = self.make_tree(self.objects, accumulator)
  File "[snip]\git-issues\gitshelve.py", line 338, in make_tree
    name = self.git('mktree', '-z', input=buf.getvalue())
  File "[snip]\git-issues\gitshelve.py", line 220, in git
    return apply(git, args, kwargs)
  File "[snip]\git-issues\gitshelve.py", line 134, in git
    raise GitError(cmd, args, kwargs, err)
gitshelve.GitError: Git command failed: git mktree (): fatal: path cb/4266b0c28c331fc69965b47242094468bd6f32/issue.xml contains slash

I'm running Windows 10, with Python 2.7.13. I got no such error when running Debian 8 with Python 2.7.9.