Adding subproject product to copy files phase

I'm not sure if this is an issue or a problem with my code but I'm attempting to create a new project, add a subproject to it and add a .bundle product of the sub project to the dependencies and the copy files phase.

Adding to dependencies works so the file references appear to be correct but adding the file to the copy files phase results in a "(null)" entry in the project.

My code is:

``` ruby
// Create a new project
proj = Xcodeproj::Project.new(outpath, false)

// Open the subproject
sublib_proj = Xcodeproj::Project.open('/Projects/Fuudey/iPhone/FuudeyLib/FuudeyLib.xcodeproj')

// Create a main group
group = proj.main_group.new_group(appname)

sub_project = group.new_file()
sub_bundle = sublib_proj.root_object.targets.select { |t| t.name == 'BundleProject' }[0]

// Add a new iOS native target
app_target = proj.new_target(:application, appname, :ios, '7.0')

// This works
app_target.add_dependency(sub_bundle)

// This doesn't
app_target.add_resources([sub_bundle.product_reference])
```

This appears to be correct from looking at the documentation but it doesn't work in practice. Am I missing something or is this a bug?

Thanks