errr... how is that possible if both the Rails 3 app and the Rails 4 app are using Bundler? I'm having trouble reproducing that scenario. In fact, in my testing, it's impossible to get the wrong one unless you delete the Gemfile with Rails 3 in it:

```
andre ~/sw/gems/bundler-testcases/binstubs-rails4/rails3 $ rails _4.0.0.beta1_ -v
Rails 3.2.13
andre ~/sw/gems/bundler-testcases/binstubs-rails4/rails3 $ rm Gemfile
andre ~/sw/gems/bundler-testcases/binstubs-rails4/rails3 $ rails _4.0.0.beta1_ -v
Rails 4.0.0.beta1
```