RubyMine and Gosu game development library

I admit I'm an almost total Ruby / RubyMine newbie, so maybe my expectations are out of whack here, but from what I have read this seems weird, and I could do with some feedback from more knowledgeable folks...

My environment:

• OS X 10.6.8
• Ruby 1.8.7
• RubyMine 3.1 (and also tried with later versions just in case, right up 4.5)

I'm trying to play around with the Gosu game development library (http://www.libgosu.org/) and so to start with installed the corresponding gem with: sudo gem install gosu

That seems to have worked. I can follow along with their tutorial materials with no bother using vim and the programs I write run just fine. The thing that is puzzling me is that RubyMine doesn't seem to recognize this gem, or perhaps I misunderstand the extent to which it can recognize and offer support (e.g. autocomplete) for a gem.

For example...consider the following code:

require 'rubygems'
require 'gosu'


class Tutorial < Gosu::Window
  def initialize
    super( 640, 480, false )
    self.caption = "Gosu Tutorial Game"
    @background_image = Gosu::Image.new( self, "media/Space.png", true )
  end

The gem is properly "attached" when I go look at Ruby SDK and Gems in Settings. I've tried detaching and reattaching a few times.

So I suppose my main question is, am I wrong to expect it to recognize Gosu, and have an understanding of inherited methods/properties that come from the Tutorial class extending Gosu::Window? Should it not be able to autocomplete identifiers from the Gosu library? I kind of imagine it should, but simply cannot seem to get it to do so.

Any explanation or suggestions would be very welcome!

Thanks,
Jon