For parented objects, the rotation, location and size keyframe are in relation to its parent.
I tried it and finally got it working Note that it only works if you rotate locally about the x axis (this is what was throwing me off for the looonngesst time).
Try it with a cube, arbitrarily tilt it and parent it to an empty for the world axis and try spinning the cube locally in the ipo editor about an axis other than x and it uses the global axis instead!
Perhaps a bug, Gimble noticed this as well – a quote from another post I found about this subject:
I believe the only way using (local) Rotation IPOs is to ensure that your object is rotating wrt its local X axis. I made an example here using a cylinder which was arbitrarily inserted at some view angle, which is parented to an Empty.
I guess I should use search more often.
Thanks for your help