Comment by iamthebest

Yeah. For example:

  $ git branch fireos
  $ git branch fireos/feature-branch
  error: unable to create directory for .git/refs/heads/fireos/feature-branch
  fatal: Failed to lock ref for update: No such file or directory

This happens because creating 'fireos' branch stores the sha1 in file .git/refs/heads/fireos. But if you later want to create branch 'fireos/feature-branch', git needs to store the sha1 in .git/refs/heads/fireos/feature-branch. This is impossible because 'fireos' is a file and cannot be a directory. Path conflict.