See, I've never seen isolationism as a key component of libertarianism. My personal readings have always shown the two key planks of libertarianism are 'smaller government' and 'let people do whatever they want, for the most part'. Foreign affairs aren't really a key part of the ideology, although most libertarians are isolationist. Ergo = interventionist libertarian.
But Libertarianism teaches that no man can force his will upon another through the use of force. Libertarianism does not support isolationism, per say, but it certainly does not support actions like the Iraq War.
Then again, this post violates my last one
"True libertarianism" strikes me more as a religion or life philosophy than a political ideology because it allows for basically no pragmatism to deal with whatever situation may arise. That's why libertarians will often argue to no end about how other other one isn't really a libertarian.
The reason I no longer identify as a Libertarian is because Libertarians argue each other to death over what a Libertarian actually is.