Originally Posted by Adlerdriver

This sounds like a cop out. I'll bet there's a clear explanation about VNAV in your manual. Claiming a "gap" is putting 100% of your training on your instructors during classroom and simulator events. You have a responsibility to study the subject matter too. Expecting everything you might encounter in the aircraft or simulator to be provided to your by someone else is unrealistic.
You clearly don't understand VNAV or you wouldn't have tried to re-cruise the box on an approach, most likely in VNAV Path and in Descent mode. Get in the books and do what's necessary to gain a working knowledge of the system so you're not just repeating behavior without any real understanding of what the expected outcome of an action will be.