Changing a git URL breaks bundle lock

[indirect]

Original Gemfile:

gem "rails3-generators", :git => "git@github.com:indirect/rails3-generators.git"

Ran bundle install; bundle lock, changed Gemfile to:

gem "rails3-generators", :git => "git://github.com/indirect/rails3-generators.git"

Got "Gemfile changed, relock" error, but running bundle lock produced:

$ bundle lock
/usr/local/Cellar/Gems/1.8/gems/bundler-0.9.9/lib/bundler/source.rb:324:in `chdir': No such file or directory - /Users/andre/.bundle/ruby/1.8/cache/bundler/git/rails3-generators-8010929e3203c4543e8d6c10de05c4b2f4b83deb (Errno::ENOENT)
    from /usr/local/Cellar/Gems/1.8/gems/bundler-0.9.9/lib/bundler/source.rb:324:in `in_cache'
    from /usr/local/Cellar/Gems/1.8/gems/bundler-0.9.9/lib/bundler/source.rb:320:in `revision'
    from /usr/local/Cellar/Gems/1.8/gems/bundler-0.9.9/lib/bundler/source.rb:264:in `lock'
    from /usr/local/Cellar/Gems/1.8/gems/bundler-0.9.9/lib/bundler/runtime.rb:59:in `lock'
    from /usr/local/Cellar/Gems/1.8/gems/bundler-0.9.9/lib/bundler/runtime.rb:59:in `each'
    from /usr/local/Cellar/Gems/1.8/gems/bundler-0.9.9/lib/bundler/runtime.rb:59:in `lock'
    from /usr/local/Cellar/Gems/1.8/gems/bundler-0.9.9/lib/bundler/cli.rb:76:in `lock'