Ruby Bundler Version Dependency Confusion in Lockfile

I will try and keep this focused.

When trying to move from a working bundler 1.14.6 combined with a Gemfile + Gemfile.lock to 1.15.2 or higher I ran into some failures in our old project's install. We believe that the failure is caused from a Gemfile.lock that is specified in a way that stricter parsing in 1.15.x and higher doesn't like. (found a vague reference to this in an issue posted somewhere on github, lost the reference. Manual resolution was recommended)

On the road to trying to fix it I am faced with trying to understand WHY it is failing and WHAT this has to do with it.

The error I am currently working on is shown below:

Downloading twitter-bootstrap-rails-2.1.0 revealed dependencies not in the API
or the lockfile (therubyracer (~> 0.10.1), less-rails (~> 2.2.2)).

Focussing on the less-rails problem, when I do a

gem list

I get the indication that less-rails is already at 2.2.4.

less-rails (2.2.4)

Why isn't the specified less-rails (~> 2.2.2) not happy with the 2.2.4 that is installed?

Please help me understand so I can take a run at fixing the other issues popping up.

Here is the gemfile and gemfile.lock that exhibits the problem.

Really struggling to understand this one, any help is appreciated. Thanks!