Rotation with manipulator sometimes changes other axes too

Sometimes when rotating an object with the rotation manipulator, values of other axes than the one dragged change too. This results in an animation that is not at all what is wanted.

If unable to reproduce with basic meshes, try the following:

• Import an FBX that has X rotation of -90 by default
• Animate rotation
• Rotate the Y axis with the rotation tool
• Observe X and Z both changing values (from -90 to 90 and from 0 to -180).

Run the animation -> the object rotates around all axes.