brew doctor is broken

gistfile1.txt

  % brew doctor                                                                                                                                                                                     !10032
Error: undefined method `head' for #<SoftwareSpec:0x100a97210>
Please report this bug:
    https://github.com/mxcl/homebrew/wiki/troubleshooting
/usr/local/Library/Formula/sphinx.rb:24
/usr/local/Library/Homebrew/formula.rb:722:in `instance_eval'
/usr/local/Library/Homebrew/formula.rb:722:in `resource'
/usr/local/Library/Formula/sphinx.rb:23
/usr/local/Library/Homebrew/formulary.rb:40:in `require'
/usr/local/Library/Homebrew/formulary.rb:40:in `klass'
/usr/local/Library/Homebrew/formulary.rb:90:in `get_formula'
/usr/local/Library/Homebrew/formulary.rb:175:in `factory'
/usr/local/Library/Homebrew/formula.rb:432:in `factory'
/usr/local/Library/Homebrew/formula.rb:384:in `installed'
/usr/local/Library/Homebrew/formula.rb:382:in `map'
/usr/local/Library/Homebrew/formula.rb:382:in `installed'
/usr/local/Library/Homebrew/cmd/doctor.rb:875:in `check_missing_deps'
/usr/local/Library/Homebrew/cmd/doctor.rb:1095:in `send'
/usr/local/Library/Homebrew/cmd/doctor.rb:1095:in `doctor'
/usr/local/Library/Homebrew/cmd/doctor.rb:1094:in `each'
/usr/local/Library/Homebrew/cmd/doctor.rb:1094:in `doctor'
/usr/local/Library/brew.rb:95:in `send'
/usr/local/Library/brew.rb:95