I've encountered this problem many a times in certain situations.
When I build 3D-things in After Effects I usually do some parenting between different solids and the likes as we all do. The problem comes though when I have parented something to an object, and then I try to rotate the parented part. It's dimensions goes amock and distorts in all ways and sizes! To the point that I can barely use it.
As an example, here's a link to an .aep that I made to test out some thoughts on a Motion Control Rig. Look at how it looks at the start and then run through the animation on the timeline. The only parameters that are animated are rotation-axis'es that are parented to each other to make up a pseudo-robotic arm thingy. The weirdest part is that the camera that is parented to the end of the arm distorts its output in an extreme way when it rotates around... I didn't even know that that was even possible?!