Yeah, you're right.

I think the docs read a little funny and I misunderstood -- I thought `FORMAT_MESSAGE_IGNORE_INSERTS` only mattered when there was something non-null passed for `va_list`.  But that appears to not be the case... 

BTW -- this is an improvement over the existing gem code we're using:
https://github.com/puppetlabs/puppet-win32-ruby/blob/ad74ee4e3e47cf039b10c4f65282da63f7e06506/ruby/lib/ruby/gems/1.9.1/gems/windows-pr-1.2.2/lib/windows/error.rb#L447