I'm happy to hear an intelligent question! 

Some time ago (two years, darn...) I ran into the same problem and started a topic about it. In short, the functions is not really broken, it's just that the problem handles rotations completely different than we would. Instead of three values, a quaternion consists of four. I'm not sure how/why, never really figured that out.

To get the 'proper' rotation values, you could rotate a vector and then calculate the separate angles. To do so, you can either use the atan2, which you'll have to add using Jestermons great RadMath dll, or use a Dot Product rule to calculate the angles between two vectors. For the last one you'll have to create 'reference vectors', aligned with the three axes.

The trick is to create three projects of the rotated vector, one in each axis, and then get the desired rotation.

I'd recommend using the atan2 variant. If you have a moment, I'll create an example.

EDIT: Forget what I said about atan2. This method works only if an object is only rotated in one axis. I found an old project using the second method. Attached below.

Hope it helps. If you have any questions, feel free to ask.