Getting NaN on iOS when using animation.

I use an Animator on a GameObject hierarchy with a clip animating the rotation of a child. Everything is fine in the editor (5.3.0.f4). On iOS the animation generates NaN for rotation and scale of that child object so that the attached sprite is not being rendered.

I reduced everything in order to find the bug.
The hierarchy is: Root->Body->Head->Jaw
Animator is attached to Root.
The animation clip does only a rotation around the z-axis starting at 20 and going to 10. So nothing special here.

An attached script logs for the Head object:
Local Rotation: (NaN, NaN, NaN, NaN)
Rotation: (NaN, NaN, NaN, NaN)
Local Scale: (1.0, 1.0, 1.0)
Scale: (NaN, NaN, NaN)

Only position seems to be fine.

If I don’t change any value within the animation (only static values) everything stays fine.

Anyone an idea what I’m doing wrong? Thanks!

Seems to work if I switch Interpolation from Euler Angles to Quaternion in the animation clip.
Is it a bug in the iOS implementation or did I miss something?

Problem still exists in 5.3.1f1.